Management

Investment manager: Legg Mason Partners Fund Advisor, LLC (“LMPFA”)

Subadvisers: Legg Mason Global Asset Allocation, LLC (“LMGAA”) and Western Asset Management Company (“Western Asset”)

Portfolio managers

LMGAA: Steven Bleiberg, Y. Wayne Lin and Patricia Duffy. Mr. Bleiberg (President and Chief Investment Officer of LMGAA) has been a portfolio manager for the fund since its inception. Mr. Lin (Chief Administrative Officer, Investment Strategy Analyst and Portfolio Manager of LMGAA) has been a portfolio manager for the fund since August 2011. Ms. Duffy (Senior Analyst and Portfolio Manager of LMGAA) has been a portfolio manager for the fund since June 2012.

Western Asset: Stephen A. Walsh and Prashant Chandran. Mr. Walsh and Mr. Chandran have been part of the portfolio management team for the fund since November 2011. These investment professionals work together with a broader investment management team. It is anticipated that Mr. Walsh will step down as a member of the fund’s portfolio management team effective on or about March 31, 2014 and that S. Kenneth Leech will join the fund’s portfolio management team at that time.

Purchase and sale of fund shares

You may purchase, redeem or exchange shares of the fund each day the New York Stock Exchange is open, at the fund’s net asset value determined after receipt of your request in good order, subject to any applicable sales charge.

Purchase and sale of fund shares cont’d

The fund’s initial and subsequent investment minimums generally are as follows:

Your financial intermediary may impose different investment minimums.

For more information about how to purchase, redeem or exchange shares, and to learn which classes of shares are available to you, you should contact your financial intermediary, or, if you hold your shares or plan to purchase shares through the fund, you should contact the fund by phone at 1-877-721-1926 or by mail at Legg Mason Funds, P.O. Box 55214, Boston, MA 02205-8504.

Tax information

The fund’s distributions are taxable as ordinary income or capital gain, except when your investment is through an IRA, 401(k) or other tax-advantaged account.

Payments to broker/dealers and other financial intermediaries

The fund’s related companies may pay broker/dealers or other financial intermediaries (such as a bank or an insurance company) for the sale of fund shares and related services. These payments create a conflict of interest by influencing your broker/dealer or other intermediary or its employees or associated persons to recommend the fund over another investment. Ask your financial adviser or salesperson or visit your financial intermediary’s or salesperson’s website for more information.

Legg Mason Target Retirement 2020

Investment objectives

The fund seeks the highest total return (that is, a combination of income and long-term capital appreciation) over time consistent with its asset mix. From the five years before until the five years after the fund’s target retirement date of 2020 (the “Dynamic Rebalancing Period”), the fund will seek to reduce volatility as a secondary objective.

Fees and expenses of the fund

The accompanying table describes the fees and expenses that you may pay if you buy and hold shares of the fund.

You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $25,000 in funds sold by Legg Mason Investor Services, LLC (“LMIS”), the fund’s distributor. More information about these and other discounts is available from your financial intermediary, in this Prospectus on page 126 under the heading “Sales charges” and in the fund’s statement of additional information (“SAI”) on page 89 under the heading “Sales Charge Waivers and Reductions.”

The fund no longer offers Class R1 shares for purchase by new or existing investors.

Example

This example is intended to help you compare the cost of investing in the fund with the cost of investing in other mutual funds. The example assumes:

Fees and expenses of the fund cont’d

Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Portfolio turnover. The fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the fund’s performance. During the most recent fiscal year, the fund’s portfolio turnover rate was 48% of the average value of its portfolio.

Principal investment strategies

The fund is a fund of funds—it invests primarily in other funds. These underlying funds are open-end funds managed by the manager or its affiliates, or exchange-traded funds (“ETFs”) that are based on an index and managed by unaffiliated investment advisers.

The fund seeks to achieve its objectives by investing in a combination of underlying funds representing a variety of broad asset classes—equity, fixed income and inflation-hedging—and investment styles. The fund is designed for investors expecting to retire around 2020. The fund’s asset mix has been designed on the expectation that investors will begin to withdraw assets from the fund during 2020, but will continue to maintain a significant portion of their investment in the fund for a period of time—perhaps 10 to 20 years—following that date. While the fund seeks to reduce volatility during the Dynamic Rebalancing Period, the fund may not achieve its goals. You should take these factors into consideration when deciding on an investment in the fund.

The fund generally seeks to maintain a certain Target Allocation, as described below. However, during the Dynamic Rebalancing Period, Legg Mason Global Asset Allocation, LLC (“LMGAA”), one of the fund’s subadvisers, in its discretion, may adjust the fund’s asset mix as often as daily and may vary the fund’s allocation substantially from the Target Allocation. The fund’s Target Allocation for equity funds (including real estate-related funds), fixed income funds and inflation-hedging funds is shown in the table below:

LMGAA is responsible for implementation of the fund’s overall asset allocation. During the fund’s Dynamic Rebalancing Period, LMGAA also manages the assets allocated to the Dynamic Risk Management strategy. Western Asset Management Company (“Western Asset”), the fund’s other subadviser, manages the assets

allocated to the Event Risk Management strategy, described below, during the fund’s Dynamic Rebalancing Period.

Glide path period

Over time, the allocation to asset classes and underlying funds will change according to a predetermined “glide path.” The glide path represents the shifting of asset classes over time. The glide path is detailed in the chart below:

During the time that the fund’s asset allocations track the glide path, the fund’s asset mix will gradually become more conservative until approximately 2035, or 15 years after the target date, at which time the asset mix will become static. This reflects the goal of pursuing the highest total return, consistent with a reasonable amount of risk, during the investor’s pre-retirement and early retirement years. By following these investment strategies after the fund reaches its target date, the fund seeks to reduce the likelihood that an investor will experience a significant loss of capital at a more advanced age.

The Target Allocations reflected in the glide path are “neutral” allocations, which do not reflect tactical decisions made by LMGAA to overweight or underweight a particular asset class. From time to time, LMGAA may make tactical increases or decreases to the fund’s investment in a particular asset class beyond the Target Allocation, based on a broad range of market and economic trends and quantitative factors. LMGAA may also allow the relative weightings of the fund’s investments in asset classes to vary from its Target Allocation in response to the markets.

Dynamic rebalancing period

During the Dynamic Rebalancing Period, the fund will not be managed strictly according to the standard Target Allocation. Instead, LMGAA will implement a combination of risk management strategies that will attempt to limit downside volatility within the fund. These strategies include Dynamic Risk Management and Event Risk Management, as described below. Through both strategies, the fund gives up some of the potential for high total return that could be achieved if the fund were to follow its Target Allocation under positive market conditions. In exchange, these strategies are intended to result in less significant declines in the fund’s net asset value (“NAV”) under negative market conditions. The fund’s NAV will fluctuate and is not guaranteed.

Dynamic risk management. The Dynamic Risk Management strategy will seek to reduce the fund’s market risk exposure and volatility. As frequently as daily, the Dynamic Risk Management strategy may increase the fund’s exposure to short-term defensive instruments (including Treasury bills, money market funds and cash) in response to certain levels of negative fund performance. At other times Dynamic Risk Management may decrease the fund’s exposure to short-term defensive instruments and increase its exposure to equity funds and long-term fixed income funds in order to return to the fund’s Target Allocation in response to certain levels of positive fund performance. The maximum daily allocation to short-term defensive instruments will be 95% of the fund’s net assets.

Principal investment strategies cont’d

In response to certain levels of negative fund performance, LMGAA may increase the fund’s exposure to short-term defensive instruments (“de-risking”) based on a formula that takes into account the fund’s current NAV, macro-economic conditions, and the fund’s underlying volatility. In order to implement this strategy, LMGAA anticipates that it will initially attempt to sell shares of ETFs and other liquid securities or engage in short sale transactions involving futures. Then, LMGAA would redeem underlying open-end mutual fund shares as needed. In response to certain levels of positive fund performance, the fund may purchase ETFs or underlying open-end mutual fund shares or cover short futures positions (when the fund is not managed strictly according to the standard Target Allocation). LMGAA, in its discretion, will determine the levels and timing for Dynamic Risk Management. If LMGAA determines that de-risking is no longer appropriate, the fund will reverse this process, sell short-term defensive instruments and purchase equity funds and long-term fixed income funds in accordance with the fund’s Target Allocation.

LMGAA may from time to time make tactical increases or decreases to the fund’s investment in a particular asset class beyond the Target Allocation based on a broad range of market and economic trends and quantitative factors. LMGAA may also allow the relative weightings of the fund’s investments in asset classes to vary from its Target Allocation in response to the markets. When varying exposures among underlying funds, LMGAA will examine relative values and prospects among the underlying funds’ asset classes, as well as the capacity of the underlying funds to absorb additional cash flow.

Event risk management. The Event Risk Management strategy will seek to reduce the impact to the fund of market declines during a short period of time caused by, for example, sudden and substantial movements in the equity markets, interest rates or credit spreads. The fund initially will invest up to 2% of its net assets in this strategy (as measured by the premiums paid on options or initial margin on futures contracts). However, the fund may invest up to 7% of its net assets at the time of purchase in this strategy (as measured by the premiums paid on options or initial margin on futures contracts). If the fund’s holdings in this strategy increase in value to over 7% of its net assets as a result of market movements, the fund will reduce, at least monthly, the amount of its assets invested in this strategy to no more than 7% of its net assets. The value of the fund’s assets invested in this strategy may be substantially higher than the value of the premiums paid or initial margin amounts on the instruments used to implement the strategy. If the value of the instruments in the Event Risk Management strategy declines after the fund has engaged in “de-risking,” the fund’s NAV could decline even if the broader markets rise in value. Conversely, if the value of the instruments in the Event Risk Management strategy increases after the fund has engaged in “de-risking,” the fund’s net asset value could increase even if the broader markets fall in value.

Western Asset’s views and outlook regarding potential unexpected market movements will determine the investments and strategies it employs in implementing the Event Risk Management strategy. During normal market conditions, the fund will implement the Event Risk Management strategy through investments in options, futures, swaps or other instruments. Since the Event Risk Management strategy seeks to primarily benefit from large and unexpected market movements, there may be times when the investment and transaction costs related to hedging will result in losses to the fund. The Event Risk Management strategy will be actively managed in an effort to reduce these costs when possible.

Static allocation period

The fund’s Target Allocation will become static 15 years after the target date. At this time, when the fund’s Target Allocation will match the Target Allocation of Legg Mason Target Retirement Fund (the “Retirement Fund”), the fund’s Board of Trustees may combine the fund with the Retirement Fund without shareholder approval, and the fund’s shareholders will become shareholders of the Retirement Fund. This is expected to occur approximately in the year 2035. This combination is expected to be tax-free under current law. Shareholders will be provided with additional information at that time.

The Retirement Fund’s Target Allocation is 33% in equity, 62% in fixed income and 5% in inflation-hedging funds.

Certain risks

Risk is inherent in all investing. There is no assurance that the fund will meet its investment objectives. The value of your investment in the fund, as well as the amount of return you receive on your investment, may fluctuate significantly. You may lose part or all of your investment in the fund or your investment may not perform as well as other similar investments. In addition, you may experience losses

near, at or after the target date. You should not rely solely on the target date when choosing to invest in the fund or deciding to remain invested in the fund. You should consider the fund’s investment strategies over the whole life of the fund. Unlike many other target retirement date funds, the fund, during the Dynamic Rebalancing Period, may not follow the Target Allocation indicated by the glide path. There is no assurance that the fund will provide sufficient retirement income at and after the target date. The following is a summary description of certain risks of investing in the fund.

Affiliated funds risk. The fund’s manager serves as manager of certain underlying funds and is affiliated with the manager of other underlying funds. In addition, the fund may invest in certain underlying funds for which LMGAA or Western Asset serve as adviser. It is possible that a conflict of interest among the fund and the underlying funds could affect how the fund’s manager, LMGAA or Western Asset fulfill their fiduciary duties to the fund and the underlying funds. For example, LMGAA may have an incentive to allocate the fund’s assets or to maintain the fund’s allocation to those funds for which the fees paid to the manager or a subadviser are higher than the fees paid by other underlying funds or to those funds for which a subadviser serves as adviser. However, the fund has adopted procedures to mitigate these concerns.

In order to implement the Dynamic Risk Management strategy, LMGAA anticipates that it will initially sell shares the fund holds in ETFs and other liquid securities or engage in short sale transactions involving index options and index futures contracts.

Then, LMGAA would redeem shares of underlying open-end mutual funds as needed. As a result, there may be conflicts of interest if unaffiliated ETFs are sold before affiliated underlying open-end mutual funds.

Allocation risk. The fund’s ability to achieve its investment objectives depends upon LMGAA’s skill in determining the fund’s asset class allocation, creating and applying formulas for de-risking or ending de-risking, determining when to engage in Event Risk Management and in selecting the best mix of underlying funds. The value of your investment may decrease if LMGAA’s judgment about the attractiveness, value or market trends affecting a particular asset class, investment style, technique or strategy, underlying fund or other issuer is incorrect.

In implementing the Dynamic Risk Management or Event Risk Management strategies, the fund will be subject to heightened allocation risk, as LMGAA will have discretion in determining the fund’s asset class allocation. If the fund increases its exposure to short-term defensive instruments at inopportune times or for extended periods of time, the fund may experience lower performance and greater losses.

Cash management and defensive investing risk. During the Dynamic Rebalancing Period, the fund may have significant exposure to short-term defensive instruments, which typically will include Treasury bills, money market funds and cash. The fund may also engage in short sale transactions involving index options and index futures contracts. The value of these investments held by the fund can fluctuate. Like other fixed income securities, they are subject to risk, including market, interest rate and credit risk. If the fund holds cash uninvested, it will be subject to the credit risk of the depository institution holding the cash. If the fund holds cash uninvested, the fund will not earn income on the cash. If the fund has a significant amount of exposure to short-term defensive instruments or the fund sells index options or index futures contracts short, it may not achieve high total returns.

Derivatives risk. Using derivatives may have a leveraging effect, which may result in a disproportionate increase in fund losses on the investment, and reduce opportunities for gains when market prices, interest rates or the derivative instruments themselves behave in a way not anticipated by the fund. Using derivatives also can increase fund volatility. Derivatives may be difficult to sell, unwind or value, and the counterparty may default on its obligations to the fund. Recent legislation calls for new regulation of the derivatives markets. The extent and impact of the regulation are not yet fully known and may not be for some time. New regulation of derivatives may make them more costly, may limit their availability, or may otherwise adversely affect their value or performance. Derivatives used for hedging purposes may have an imperfect correlation to the assets held by the fund and may not adequately protect against losses in or may result in greater losses for the fund’s portfolio.

Dynamic risk management strategy risk. In implementing the Dynamic Risk Management strategy, LMGAA anticipates that it will initially sell shares the fund holds in ETFs and other liquid securities or engage in short sale transactions involving index options and index futures contracts. Then, LMGAA would redeem shares of underlying open-end mutual funds as needed. As a result, the fund’s assets may be more concentrated in its

Certain risks cont’d

underlying mutual fund holdings. In addition, during periods of market volatility, the share prices of ETFs may deviate significantly from their NAVs. Therefore, selling shares of ETFs during periods of market volatility may result in greater losses than redeeming open-end mutual fund holdings. Similarly, the use of derivatives may cause the fund to experience greater losses than redeeming mutual fund holdings. The fund may incur additional trading costs while implementing the Dynamic Risk Management strategy, which may reduce the fund’s performance. There is no guarantee that the Dynamic Risk Management strategy will work and shareholders should evaluate their ability to invest for the long-term, especially during periods of downturn in the market.

Event risk management strategy risk. The Event Risk Management strategy may involve entering into transactions involving options, futures and swaps that are expected to increase in value during the occurrence of certain market events. An instrument used to hedge market event risk could lose all or a portion of its value even in a period of severe market stress. Implementation of the strategy may result in the fund holding options and futures positions that take contradictory views on market movements. The costs of purchasing and selling these instruments may reduce the fund’s return. The fund may not be able to close out a position at the desired time or price. There is no guarantee that the Event Risk Management strategy will work and shareholders should evaluate their ability to invest for the long term, especially during periods of downturn in the market.

Tax risk. The fund’s hedging strategy may result in the fund deferring, possibly indefinitely, certain of its realized losses for U.S. federal income tax purposes, potentially increasing the amount of the fund’s taxable distributions paid to shareholders.

Short sales risk. A short sale of a security involves the risk that instead of declining, the price of the security sold short will rise. If the price of the security sold short increases between the time of the short sale and the time the fund replaces the borrowed security, the fund will realize a loss. The short sale of securities involves the possibility of a theoretically unlimited loss since there is a theoretically unlimited potential for the market price of the security sold short to increase. Shorting futures may have an imperfect correlation to the assets held by the fund and may not adequately protect against losses in or may result in greater losses for the fund’s portfolio.

Segregated assets risk. In connection with certain transactions that may give rise to future payment obligations, including many types of derivatives, the fund may be required to maintain a segregated amount of cash or liquid securities to cover the position. Segregated securities cannot be sold while the position they are covering is outstanding, unless they are replaced with other securities of equal value. As a result, there is the possibility that segregation of a large percentage of the fund’s assets, in some circumstances, may limit the subadvisers’ flexibility.

Asset class variation risk. The underlying funds invest principally in the securities constituting their asset class ( i.e. , equity, fixed income, inflation-hedging investments and short-term defensive instruments). However, under normal market conditions, an underlying fund may vary the percentage of its assets in these securities (subject to any applicable regulatory requirements). Depending upon the percentage of securities in a particular asset class held by the underlying funds at any given time and the percentage of the fund’s assets invested in various underlying funds, the fund’s actual exposure to the securities in a particular asset class may vary substantially from its Target Allocation for that asset class.

Fund of funds risk. Your cost of investing in the fund, as a fund of funds, may be higher than the cost of investing in a mutual fund that only invests directly in individual securities. An underlying fund may change its investment objective or policies without the fund’s approval, which could force the fund to withdraw its investment from such underlying fund at a time that is unfavorable to the fund. In addition, one underlying fund may buy the same securities that another underlying fund sells. Therefore, the fund would indirectly bear the costs of these trades without accomplishing any investment purpose.

Stock market and equity securities risk. The securities markets are volatile and the market prices of the fund’s or underlying fund’s securities may decline generally. Securities fluctuate in price based on changes in a company’s financial condition and overall market and economic conditions. If the market prices of the securities owned by the fund or underlying fund fall, the value of your investment in the fund will decline. The financial crisis that began in 2008 has caused a significant decline in the value and liquidity of many securities of issuers worldwide. In response to the crisis, the U.S. and other governments and the Federal Reserve and certain foreign central banks have taken steps to support

financial markets. These market conditions may continue, worsen or spread, including in the United States, Europe and beyond. The withdrawal of this support, failure of efforts to respond to the crisis, or investor perception that such efforts are not succeeding could also negatively affect financial markets generally as well as the value and liquidity of certain securities. Whether or not the fund or underlying fund invests in securities of issuers located in or with significant exposure to countries experiencing economic and financial difficulties, the value and liquidity of the fund’s or underlying fund’s investments may be negatively affected by the conditions in the countries experiencing the difficulties. In addition, policy and legislative changes in the United States and in other countries are changing many aspects of financial regulation. The impact of these changes on the markets, and the practical implications for market participants, may not be fully known for some time.

Fixed income securities risk. Fixed income securities are subject to a number of risks, including credit, market and interest rate risks. Credit risk is the risk that the issuer or obligor will not make timely payments of principal and interest. Changes in an issuer’s credit rating or the market’s perception of an issuer’s creditworthiness may also affect the value of an underlying fund’s investment in that issuer. Market risk is the risk that the fixed income markets may become volatile and less liquid, and the market value of an investment may move up or down, sometimes quickly or unpredictably. Interest rate risk is the risk that the value of a fixed income security will fall when interest rates rise. In general, the longer the maturity and the lower the credit quality of a fixed income security, the more likely its value will decline.

Issuer risk. The value of a security can go up or down more than the market as a whole and can perform differently from the value of the market as a whole, often due to disappointing earnings reports by the issuer, unsuccessful products or services, loss of major customers, major litigation against the issuer or changes in government regulations affecting the issuer or the competitive environment. An underlying fund may experience a substantial or complete loss on an individual security. Historically, the prices of securities of small and medium capitalization companies have generally gone up or down more than those of large capitalization companies, although even large capitalization companies may fall out of favor with investors.

Large capitalization company risk. Large capitalization companies may fall out of favor with investors.

Small and medium capitalization company risk. An underlying fund will be exposed to additional risks as a result of its investments in the securities of small and medium capitalization companies. Small and medium capitalization companies may fall out of favor with investors; may have limited product lines, operating histories, markets or financial resources; or may be dependent upon a limited management group. The prices of securities of small and medium capitalization companies generally are more volatile than those of large capitalization companies and are more likely to be adversely affected than large capitalization companies by changes in earnings results and investor expectations or poor economic or market conditions, including those experienced during a recession. Securities of small and medium capitalization companies may underperform large capitalization companies, may be harder to sell at times and at prices an underlying fund’s adviser believes appropriate and may offer greater potential for losses.

Liquidity risk. Some assets or derivatives held by the fund or an underlying fund or futures sold by the fund or an underlying fund may be difficult to sell, or illiquid, particularly during times of market turmoil. Illiquid assets or derivatives may also be difficult to value. If the fund or an underlying fund is forced to sell an illiquid asset to meet redemption requests or other cash needs, the fund or an underlying fund may be forced to sell at a loss.

Growth and value investing risk. Growth or value securities as a group may be out of favor and underperform the overall equity market while the market concentrates on other types of securities. Growth securities typically are very sensitive to market movements because their market prices tend to reflect future expectations. When it appears those expectations will not be met, the prices of growth securities typically fall. The value approach to investing involves the risk that stocks may remain undervalued. An underlying fund may, like many growth or value funds, weight its investments toward certain industries, thus increasing its exposure to factors adversely affecting issuers within those industries and, indirectly, the fund’s exposure to those factors.

Foreign investment risk. The fund or an underlying fund’s investments in securities of foreign issuers or issuers with significant exposure to foreign markets involve additional risk. Foreign countries in which

Certain risks cont’d

the fund or an underlying fund may invest may have markets that are less liquid, less regulated and more volatile than U.S. markets. The value of the fund or an underlying fund’s investments may decline because of factors affecting the particular issuer as well as foreign markets and issuers generally, such as unfavorable government actions, and political or financial instability. Lack of information may also affect the value of these securities.

The risks of foreign investments are heightened when investing in issuers in emerging market countries.

Currency risk. The value of investments in securities denominated in foreign currencies increases or decreases as the rates of exchange between those currencies and the U.S. dollar change. Currency conversion costs and currency fluctuations could erase investment gains or add to investment losses. Currency exchange rates can be volatile, and are affected by factors such as general economic conditions, the actions of the U.S. and foreign governments or central banks, the imposition of currency controls and speculation.

Real estate investment trusts (REITs) risk. Investments in REITs expose an underlying fund to risks similar to investing directly in real estate, such as changes in the value of the underlying real estate, the quality of the property management, the creditworthiness of the issuer of the investments, and changes in property taxes, interest rates and the real estate regulatory environment.

Exchange-traded funds (ETFs) risk. Investing in an ETF will give the fund exposure to the securities comprising the index on which the ETF is based and will expose the fund to risks similar to those of investing directly in those securities. Shares of ETFs are traded on an exchange and may trade at either a premium or discount to NAV. The fund will pay brokerage commissions in connection with the purchase and sale of shares of ETFs.

Valuation risk. The sales price the fund or an underlying fund could receive for any particular portfolio investment may differ from the fund’s valuation of the investment, particularly for securities or other instruments that trade in thin or volatile markets or that are valued using a fair value methodology. Investors who purchase or redeem fund shares on days when the fund or an underlying fund is holding fair-valued securities may receive fewer or more shares or lower or higher redemption proceeds than they would have received if the fund or the underlying fund had not fair-valued the security or had used a different valuation methodology.

Risk of increase in expenses. Your actual costs of investing in the fund may be higher than the expenses shown in “Annual fund operating expenses” for a variety of reasons. For example, expense ratios may be higher than those shown if a fee limitation is changed or terminated or if average net assets decrease. Net assets are more likely to decrease and fund expense ratios are more likely to increase when markets are volatile. In addition, after the fund reaches the target date, it is expected that the assets will decline as investors begin to withdraw their assets from the fund, causing gross expenses to increase.

These risks are discussed in more detail later in this Prospectus or in the SAI.

Management

Investment manager: Legg Mason Partners Fund Advisor, LLC (“LMPFA”)

Subadvisers: Legg Mason Global Asset Allocation, LLC (“LMGAA”) and Western Asset Management Company (“Western Asset”)

Portfolio managers

LMGAA: Steven Bleiberg, Y. Wayne Lin and Patricia Duffy. Mr. Bleiberg (President and Chief Investment Officer of LMGAA) has been a portfolio manager for the fund since its inception. Mr. Lin (Chief Administrative Officer, Investment Strategy Analyst and Portfolio Manager of LMGAA) has been a portfolio manager for the fund since August 2011. Ms. Duffy (Senior Analyst and Portfolio Manager of LMGAA) has been a portfolio manager for the fund since June 2012.

Western Asset: Stephen A. Walsh and Prashant Chandran. Mr. Walsh and Mr. Chandran have been part of portfolio management team for the fund since November 2011. These investment professionals work together with a broader investment management team. It is anticipated that Mr. Walsh will step down as a member of the fund’s portfolio management team effective on or about March 31, 2014 and that S. Kenneth Leech will join the fund’s portfolio management team at that time.

Purchase and sale of fund shares

You may purchase, redeem or exchange shares of the fund each day the New York Stock Exchange is open, at the fund’s net asset value determined after receipt of your request in good order, subject to any applicable sales charge.

Your financial intermediary may impose different investment minimums.

For more information about how to purchase, redeem or exchange shares, and to learn which classes of shares are available to you, you should contact your financial intermediary, or, if you hold your shares or plan to purchase shares through the fund, you should contact the fund by phone at 1-877-721-1926 or by mail at Legg Mason Funds, P.O. Box 55214, Boston, MA 02205-8504.

Tax information

The fund’s distributions are taxable as ordinary income or capital gain, except when your investment is through an IRA, 401(k) or other tax-advantaged account.

Payments to broker/dealers and other financial intermediaries

The fund’s related companies may pay broker/dealers or other financial intermediaries (such as a bank or an insurance company) for the sale of fund shares and related services. These payments create a conflict of interest by influencing your broker/dealer or other intermediary or its employees or associated persons to recommend the fund over another investment. Ask your financial adviser or salesperson or visit your financial intermediary’s or salesperson’s website for more information.

Legg Mason Target Retirement 2025

Investment objectives

The fund seeks the highest total return (that is, a combination of income and long-term capital appreciation) over time consistent with its asset mix. From the five years before until the five years after the fund’s target retirement date of 2025 (the “Dynamic Rebalancing Period”), the fund will seek to reduce volatility as a secondary objective.

Fees and expenses of the fund

The accompanying table describes the fees and expenses that you may pay if you buy and hold shares of the fund.

You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $25,000 in funds sold by Legg Mason Investor Services, LLC (“LMIS”), the fund’s distributor. More information about these and other discounts is available from your financial intermediary, in this Prospectus on page 126 under the heading “Sales charges” and in the fund’s statement of additional information (“SAI”) on page 89 under the heading “Sales Charge Waivers and Reductions.”

The fund no longer offers Class R1 shares for purchase by new or existing investors.

Example

This example is intended to help you compare the cost of investing in the fund with the cost of investing in other mutual funds. The example assumes:

Portfolio turnover. The fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the fund’s performance. During the most recent fiscal year, the fund’s portfolio turnover rate was 30% of the average value of its portfolio.

Principal investment strategies

The fund is a fund of funds—it invests primarily in other funds. These underlying funds are open-end funds managed by the manager or its affiliates, or exchange-traded funds (“ETFs”) that are based on an index and managed by unaffiliated investment advisers.

The fund seeks to achieve its objectives by investing in a combination of underlying funds representing a variety of broad asset classes—equity, fixed income and inflation-hedging—and investment styles. The fund is designed for investors expecting to retire around 2025. The fund’s asset mix has been designed on the expectation that investors will begin to withdraw assets from the fund during 2025, but will continue to maintain a significant portion of their investment in the fund for a period of time—perhaps 10 to 20 years—following that date. While the fund seeks to reduce volatility during the Dynamic Rebalancing Period, the fund may not achieve its goals. You should take these factors into consideration when deciding on an investment in the fund.

The fund generally seeks to maintain a certain Target Allocation, as described below. However, during the Dynamic Rebalancing Period, Legg Mason Global Asset Allocation, LLC (“LMGAA”), one of the fund’s subadvisers, in its discretion, may adjust the fund’s asset mix as often as daily and may vary the fund’s allocation substantially from the Target Allocation. The fund’s Target Allocation for equity funds (including real estate-related funds), fixed income funds and inflation-hedging funds is shown in the table below:

LMGAA is responsible for implementation of the fund’s overall asset allocation. During the fund’s Dynamic Rebalancing Period, LMGAA also manages the assets allocated to the Dynamic Risk Management strategy. Western Asset Management Company (“Western Asset”), the fund’s other subadviser, manages the assets allocated to the Event Risk Management strategy, described below, during the fund’s Dynamic Rebalancing Period.

Principal investment strategies cont’d

Glide path period

Over time, the allocation to asset classes and underlying funds will change according to a predetermined “glide path.” The glide path represents the shifting of asset classes over time. The glide path is detailed in the chart below:

During the time that the fund’s asset allocations track the glide path, the fund’s asset mix will gradually become more conservative until approximately 2040, or 15 years after the target date, at which time the asset mix will become static. This reflects the goal of pursuing the highest total return, consistent with a reasonable amount of risk, during the investor’s pre-retirement and early retirement years. By following these investment strategies after the fund reaches its target date, the fund seeks to reduce the likelihood that an investor will experience a significant loss of capital at a more advanced age.

The Target Allocations reflected in the glide path are “neutral” allocations, which do not reflect tactical decisions made by LMGAA to overweight or underweight a particular asset class. From time to time, LMGAA may make tactical increases or decreases to the fund’s investment in a particular asset class beyond the Target Allocation, based on a broad range of market and economic trends and quantitative factors. LMGAA may also allow the relative weightings of the fund’s investments in asset classes to vary from its Target Allocation in response to the markets.

Dynamic rebalancing period

During the Dynamic Rebalancing Period, the fund will not be managed strictly according to the standard Target Allocation. Instead, LMGAA will implement a combination of risk management strategies that will attempt to limit downside volatility within the fund. These strategies include Dynamic Risk Management and Event Risk Management, as described below. Through both strategies, the fund gives up some of the potential for high total return that could be achieved if the fund were to follow its Target Allocation under positive market conditions. In exchange, these strategies are intended to result in less significant declines in the fund’s net asset value (“NAV”) under negative market conditions. The fund’s NAV will fluctuate and is not guaranteed.

Dynamic risk management. The Dynamic Risk Management strategy will seek to reduce the fund’s market risk exposure and volatility. As frequently as daily, the Dynamic Risk Management strategy may increase the fund’s exposure to short-term defensive instruments (including Treasury bills, money market funds and cash) in response to certain levels of negative fund performance. At other times Dynamic Risk Management may decrease the fund’s exposure to short-term defensive instruments and increase its exposure to equity funds and long-term fixed income funds in order to return to the fund’s Target Allocation in response to certain levels of positive fund performance. The maximum daily allocation to short-term defensive instruments will be 95% of the fund’s net assets.

In response to certain levels of negative fund performance, LMGAA may increase the fund’s exposure to short-term defensive instruments (“de-risking”) based on a formula that takes into account the fund’s current NAV, macro-economic conditions, and the fund’s underlying volatility. In

order to implement this strategy, LMGAA anticipates that it will initially attempt to sell shares of ETFs and other liquid securities or engage in short sale transactions involving futures. Then, LMGAA would redeem underlying open-end mutual fund shares as needed. In response to certain levels of positive fund performance, the fund may purchase ETFs or underlying open-end mutual fund shares or cover short futures positions (when the fund is not managed strictly according to the standard Target Allocation). LMGAA, in its discretion, will determine the levels and timing for Dynamic Risk Management. If LMGAA determines that de-risking is no longer appropriate, the fund will reverse this process, sell short-term defensive instruments and purchase equity funds and long-term fixed income funds in accordance with the fund’s Target Allocation.

LMGAA may from time to time make tactical increases or decreases to the fund’s investment in a particular asset class beyond the Target Allocation based on a broad range of market and economic trends and quantitative factors. LMGAA may also allow the relative weightings of the fund’s investments in asset classes to vary from its Target Allocation in response to the markets. When varying exposures among underlying funds, LMGAA will examine relative values and prospects among the underlying funds’ asset classes, as well as the capacity of the underlying funds to absorb additional cash flow.

Event risk management. The Event Risk Management strategy will seek to reduce the impact to the fund of market declines during a short period of time caused by, for example, sudden and substantial movements in the equity markets, interest rates or credit spreads. The fund initially will invest up to 2% of its net assets in this strategy (as measured by the premiums paid on options or initial margin on futures contracts). However, the fund may invest up to 7% of its net assets at the time of purchase in this strategy (as measured by the premiums paid on options or initial margin on futures contracts). If the fund’s holdings in this strategy increase in value to over 7% of its net assets as a result of market movements, the fund will reduce, at least monthly, the amount of its assets invested in this strategy to no more than 7% of its net assets. The value of the fund’s assets invested in this strategy may be substantially higher than the value of the premiums paid or initial margin amounts on the instruments used to implement the strategy. If the value of the instruments in the Event Risk Management strategy declines after the fund has engaged in “de-risking,” the fund’s NAV could decline even if the broader markets rise in value. Conversely, if the value of the instruments in the Event Risk Management strategy increases after the fund has engaged in “de-risking,” the fund’s net asset value could increase even if the broader markets fall in value.

Western Asset’s views and outlook regarding potential unexpected market movements will determine the investments and strategies it employs in implementing the Event Risk Management strategy. During normal market conditions, the fund will implement the Event Risk Management strategy through investments in options, futures, swaps or other instruments. Since the Event Risk Management strategy seeks to primarily benefit from large and unexpected market movements, there may be times when the investment and transaction costs related to hedging will result in losses to the fund. The Event Risk Management strategy will be actively managed in an effort to reduce these costs when possible.

Static allocation period

The fund’s Target Allocation will become static 15 years after the target date. At this time, when the fund’s Target Allocation will match the Target Allocation of Legg Mason Target Retirement Fund (the “Retirement Fund”), the fund’s Board of Trustees may combine the fund with the Retirement Fund without shareholder approval, and the fund’s shareholders will become shareholders of the Retirement Fund. This is expected to occur approximately in the year 2040. This combination is expected to be tax-free under current law. Shareholders will be provided with additional information at that time.

The Retirement Fund’s Target Allocation is 33% in equity, 62% in fixed income and 5% in inflation-hedging funds.

Certain risks

Risk is inherent in all investing. There is no assurance that the fund will meet its investment objectives. The value of your investment in the fund, as well as the amount of return you receive on your investment, may fluctuate significantly. You may lose part or all of your investment in the fund or your investment may not perform as well as other similar investments. In addition, you may experience losses near, at or after the target date. You should not rely solely on the target date when choosing to invest in the fund or deciding to remain invested in the fund. You should consider the fund’s investment strategies over the whole life of the fund. Unlike many other target retirement date funds, the fund, during the

Certain risks cont’d

Dynamic Rebalancing Period, may not follow the Target Allocation indicated by the glide path. There is no assurance that the fund will provide sufficient retirement income at and after the target date. The following is a summary description of certain risks of investing in the fund.

Affiliated funds risk. The fund’s manager serves as manager of certain underlying funds and is affiliated with the manager of other underlying funds. In addition, the fund may invest in certain underlying funds for which LMGAA or Western Asset serve as adviser. It is possible that a conflict of interest among the fund and the underlying funds could affect how the fund’s manager, LMGAA or Western Asset fulfill their fiduciary duties to the fund and the underlying funds. For example, LMGAA may have an incentive to allocate the fund’s assets or to maintain the fund’s allocation to those funds for which the fees paid to the manager or a subadviser are higher than the fees paid by other underlying funds or to those funds for which a subadviser serves as adviser. However, the fund has adopted procedures to mitigate these concerns.

In order to implement the Dynamic Risk Management strategy, LMGAA anticipates that it will initially sell shares the fund holds in ETFs and other liquid securities or engage in short sale transactions involving index options and index futures contracts.

Then, LMGAA would redeem shares of underlying open-end mutual funds as needed. As a result, there may be conflicts of interest if unaffiliated ETFs are sold before affiliated underlying open-end mutual funds.

Allocation risk. The fund’s ability to achieve its investment objectives depends upon LMGAA’s skill in determining the fund’s asset class allocation, creating and applying formulas for de-risking or ending de-risking, determining when to engage in Event Risk Management and in selecting the best mix of underlying funds. The value of your investment may decrease if LMGAA’s judgment about the attractiveness, value or market trends affecting a particular asset class, investment style, technique or strategy, underlying fund or other issuer is incorrect.

In implementing the Dynamic Risk Management or Event Risk Management strategies, the fund will be subject to heightened allocation risk, as LMGAA will have discretion in determining the fund’s asset class allocation. If the fund increases its exposure to short-term defensive instruments at inopportune times or for extended periods of time, the fund may experience lower performance and greater losses.

Cash management and defensive investing risk. During the Dynamic Rebalancing Period, the fund may have significant exposure to short-term defensive instruments, which typically will include Treasury bills, money market funds and cash. The fund may also engage in short sale transactions involving index options and index futures contracts. The value of these investments held by the fund can fluctuate. Like other fixed income securities, they are subject to risk, including market, interest rate and credit risk. If the fund holds cash uninvested, it will be subject to the credit risk of the depository institution holding the cash. If the fund holds cash uninvested, the fund will not earn income on the cash. If the fund has a significant amount of exposure to short-term defensive instruments or the fund sells index options or index futures contracts short, it may not achieve high total returns.

Derivatives risk. Using derivatives may have a leveraging effect, which may result in a disproportionate increase in fund losses on the investment, and reduce opportunities for gains when market prices, interest rates or the derivative instruments themselves behave in a way not anticipated by the fund. Using derivatives also can increase fund volatility. Derivatives may be difficult to sell, unwind or value, and the counterparty may default on its obligations to the fund. Recent legislation calls for new regulation of the derivatives markets. The extent and impact of the regulation are not yet fully known and may not be for some time. New regulation of derivatives may make them more costly, may limit their availability, or may otherwise adversely affect their value or performance. Derivatives used for hedging purposes may have an imperfect correlation to the assets held by the fund and may not adequately protect against losses in or may result in greater losses for the fund’s portfolio.

Dynamic risk management strategy risk. In implementing the Dynamic Risk Management strategy, LMGAA anticipates that it will initially sell shares the fund holds in ETFs and other liquid securities or engage in short sale transactions involving index options and index futures contracts. Then, LMGAA would redeem shares of underlying open-end mutual funds as needed. As a result, the fund’s assets may be more concentrated in its underlying mutual fund holdings. In addition, during periods of market volatility, the share prices of ETFs may deviate significantly from their NAVs. Therefore, selling shares of ETFs during periods of market volatility may result in greater losses than redeeming open-end mutual fund holdings. Similarly, the use of derivatives may cause the fund to experience greater

losses than redeeming mutual fund holdings. The fund may incur additional trading costs while implementing the Dynamic Risk Management strategy, which may reduce the fund’s performance. There is no guarantee that the Dynamic Risk Management strategy will work and shareholders should evaluate their ability to invest for the long-term, especially during periods of downturn in the market.

Event risk management strategy risk. The Event Risk Management strategy may involve entering into transactions involving options, futures and swaps that are expected to increase in value during the occurrence of certain market events. An instrument used to hedge market event risk could lose all or a portion of its value even in a period of severe market stress. Implementation of the strategy may result in the fund holding options and futures positions that take contradictory views on market movements. The costs of purchasing and selling these instruments may reduce the fund’s return. The fund may not be able to close out a position at the desired time or price. There is no guarantee that the Event Risk Management strategy will work and shareholders should evaluate their ability to invest for the long term, especially during periods of downturn in the market.

Tax risk. The fund’s hedging strategy may result in the fund deferring, possibly indefinitely, certain of its realized losses for U.S. federal income tax purposes, potentially increasing the amount of the fund’s taxable distributions paid to shareholders.

Short sales risk. A short sale of a security involves the risk that instead of declining, the price of the security sold short will rise. If the price of the security sold short increases between the time of the short sale and the time the fund replaces the borrowed security, the fund will realize a loss. The short sale of securities involves the possibility of a theoretically unlimited loss since there is a theoretically unlimited potential for the market price of the security sold short to increase. Shorting futures may have an imperfect correlation to the assets held by the fund and may not adequately protect against losses in or may result in greater losses for the fund’s portfolio.

Segregated assets risk. In connection with certain transactions that may give rise to future payment obligations, including many types of derivatives, the fund may be required to maintain a segregated amount of cash or liquid securities to cover the position. Segregated securities cannot be sold while the position they are covering is outstanding, unless they are replaced with other securities of equal value. As a result, there is the possibility that segregation of a large percentage of the fund’s assets, in some circumstances, may limit the subadvisers’ flexibility.

Asset class variation risk. The underlying funds invest principally in the securities constituting their asset class ( i.e. , equity, fixed income, inflation-hedging investments and short-term defensive instruments). However, under normal market conditions, an underlying fund may vary the percentage of its assets in these securities (subject to any applicable regulatory requirements). Depending upon the percentage of securities in a particular asset class held by the underlying funds at any given time and the percentage of the fund’s assets invested in various underlying funds, the fund’s actual exposure to the securities in a particular asset class may vary substantially from its Target Allocation for that asset class.

Fund of funds risk. Your cost of investing in the fund, as a fund of funds, may be higher than the cost of investing in a mutual fund that only invests directly in individual securities. An underlying fund may change its investment objective or policies without the fund’s approval, which could force the fund to withdraw its investment from such underlying fund at a time that is unfavorable to the fund. In addition, one underlying fund may buy the same securities that another underlying fund sells. Therefore, the fund would indirectly bear the costs of these trades without accomplishing any investment purpose.

Stock market and equity securities risk. The securities markets are volatile and the market prices of the fund’s or underlying fund’s securities may decline generally. Securities fluctuate in price based on changes in a company’s financial condition and overall market and economic conditions. If the market prices of the securities owned by the fund or underlying fund fall, the value of your investment in the fund will decline. The financial crisis that began in 2008 has caused a significant decline in the value and liquidity of many securities of issuers worldwide. In response to the crisis, the U.S. and other governments and the Federal Reserve and certain foreign central banks have taken steps to support financial markets. These market conditions may continue, worsen or spread, including in the United States, Europe and beyond. The withdrawal of this support, failure of efforts to respond to the crisis, or investor perception that such efforts are not succeeding could also negatively affect financial markets generally as well as the value and liquidity

Certain risks cont’d

of certain securities. Whether or not the fund or underlying fund invests in securities of issuers located in or with significant exposure to countries experiencing economic and financial difficulties, the value and liquidity of the fund’s or underlying fund’s investments may be negatively affected by the conditions in the countries experiencing the difficulties. In addition, policy and legislative changes in the United States and in other countries are changing many aspects of financial regulation. The impact of these changes on the markets, and the practical implications for market participants, may not be fully known for some time.

Fixed income securities risk. Fixed income securities are subject to a number of risks, including credit, market and interest rate risks. Credit risk is the risk that the issuer or obligor will not make timely payments of principal and interest. Changes in an issuer’s credit rating or the market’s perception of an issuer’s creditworthiness may also affect the value of an underlying fund’s investment in that issuer. Market risk is the risk that the fixed income markets may become volatile and less liquid, and the market value of an investment may move up or down, sometimes quickly or unpredictably. Interest rate risk is the risk that the value of a fixed income security will fall when interest rates rise. In general, the longer the maturity and the lower the credit quality of a fixed income security, the more likely its value will decline.

Issuer risk. The value of a security can go up or down more than the market as a whole and can perform differently from the value of the market as a whole, often due to disappointing earnings reports by the issuer, unsuccessful products or services, loss of major customers, major litigation against the issuer or changes in government regulations affecting the issuer or the competitive environment. An underlying fund may experience a substantial or complete loss on an individual security. Historically, the prices of securities of small and medium capitalization companies have generally gone up or down more than those of large capitalization companies, although even large capitalization companies may fall out of favor with investors.

Large capitalization company risk. Large capitalization companies may fall out of favor with investors.

Small and medium capitalization company risk. An underlying fund will be exposed to additional risks as a result of its investments in the securities of small and medium capitalization companies. Small and medium capitalization companies may fall out of favor with investors; may have limited product lines, operating histories, markets or financial resources; or may be dependent upon a limited management group. The prices of securities of small and medium capitalization companies generally are more volatile than those of large capitalization companies and are more likely to be adversely affected than large capitalization companies by changes in earnings results and investor expectations or poor economic or market conditions, including those experienced during a recession. Securities of small and medium capitalization companies may underperform large capitalization companies, may be harder to sell at times and at prices an underlying fund’s adviser believes appropriate and may offer greater potential for losses.

Liquidity risk. Some assets or derivatives held by the fund or an underlying fund or futures sold by the fund or an underlying fund may be difficult to sell, or illiquid, particularly during times of market turmoil. Illiquid assets or derivatives may also be difficult to value. If the fund or an underlying fund is forced to sell an illiquid asset to meet redemption requests or other cash needs, the fund or an underlying fund may be forced to sell at a loss.

Growth and value investing risk. Growth or value securities as a group may be out of favor and underperform the overall equity market while the market concentrates on other types of securities. Growth securities typically are very sensitive to market movements because their market prices tend to reflect future expectations. When it appears those expectations will not be met, the prices of growth securities typically fall. The value approach to investing involves the risk that stocks may remain undervalued. An underlying fund may, like many growth or value funds, weight its investments toward certain industries, thus increasing its exposure to factors adversely affecting issuers within those industries and, indirectly, the fund’s exposure to those factors.

Foreign investment risk. The fund or an underlying fund’s investments in securities of foreign issuers or issuers with significant exposure to foreign markets involve additional risk. Foreign countries in which the fund or an underlying fund may invest may have markets that are less liquid, less regulated and more volatile than U.S. markets. The value of the fund or an underlying fund’s investments may decline because of factors affecting the particular issuer as well as foreign markets and issuers generally, such as unfavorable government actions, and political or financial instability. Lack of information may also affect the value of these securities.

The risks of foreign investments are heightened when investing in issuers in emerging market countries.

Currency risk. The value of investments in securities denominated in foreign currencies increases or decreases as the rates of exchange between those currencies and the U.S. dollar change. Currency conversion costs and currency fluctuations could erase investment gains or add to investment losses. Currency exchange rates can be volatile, and are affected by factors such as general economic conditions, the actions of the U.S. and foreign governments or central banks, the imposition of currency controls and speculation.

Real estate investment trusts (REITs) risk. Investments in REITs expose an underlying fund to risks similar to investing directly in real estate, such as changes in the value of the underlying real estate, the quality of the property management, the creditworthiness of the issuer of the investments, and changes in property taxes, interest rates and the real estate regulatory environment.

Exchange-traded funds (ETFs) risk. Investing in an ETF will give the fund exposure to the securities comprising the index on which the ETF is based and will expose the fund to risks similar to those of investing directly in those securities. Shares of ETFs are traded on an exchange and may trade at either a premium or discount to NAV. The fund will pay brokerage commissions in connection with the purchase and sale of shares of ETFs.

Valuation risk. The sales price the fund or an underlying fund could receive for any particular portfolio investment may differ from the fund’s valuation of the investment, particularly for securities or other instruments that trade in thin or volatile markets or that are valued using a fair value methodology. Investors who purchase or redeem fund shares on days when the fund or an underlying fund is holding fair-valued securities may receive fewer or more shares or lower or higher redemption proceeds than they would have received if the fund or the underlying fund had not fair-valued the security or had used a different valuation methodology.

Risk of increase in expenses. Your actual costs of investing in the fund may be higher than the expenses shown in “Annual fund operating expenses” for a variety of reasons. For example, expense ratios may be higher than those shown if a fee limitation is changed or terminated or if average net assets decrease. Net assets are more likely to decrease and fund expense ratios are more likely to increase when markets are volatile. In addition, after the fund reaches the target date, it is expected that the assets will decline as investors begin to withdraw their assets from the fund, causing gross expenses to increase.

These risks are discussed in more detail later in this Prospectus or in the SAI.

Management

Investment manager: Legg Mason Partners Fund Advisor, LLC (“LMPFA”)

Subadvisers: Legg Mason Global Asset Allocation, LLC (“LMGAA”) and Western Asset Management Company (“Western Asset”)

Portfolio managers

LMGAA: Steven Bleiberg, Y. Wayne Lin and Patricia Duffy. Mr. Bleiberg (President and Chief Investment Officer of LMGAA) has been a portfolio manager for the fund since its inception. Mr. Lin (Chief Administrative Officer, Investment Strategy Analyst and Portfolio Manager of LMGAA) has been a portfolio manager for the fund since August 2011. Ms. Duffy (Senior Analyst and Portfolio Manager of LMGAA) has been a portfolio manager for the fund since June 2012.

Western Asset: Stephen A. Walsh and Prashant Chandran. Mr. Walsh and Mr. Chandran have been part of the portfolio management team for the fund since November 2011. These investment professionals work together with a broader investment management team. It is anticipated that Mr. Walsh will step down as a member of the fund’s portfolio management team effective on or about March 31, 2014 and that S. Kenneth Leech will join the fund’s portfolio management team at that time.

Purchase and sale of fund shares

You may purchase, redeem or exchange shares of the fund each day the New York Stock Exchange is open, at the fund’s net asset value determined after receipt of your request in good order, subject to any applicable sales charge.

Purchase and sale of fund shares cont’d

The fund’s initial and subsequent investment minimums generally are as follows:

Your financial intermediary may impose different investment minimums.

For more information about how to purchase, redeem or exchange shares, and to learn which classes of shares are available to you, you should contact your financial intermediary, or, if you hold your shares or plan to purchase shares through the fund, you should contact the fund by phone at 1-877-721-1926 or by mail at Legg Mason Funds, P.O. Box 55214, Boston, MA 02205-8504.

Tax information

The fund’s distributions are taxable as ordinary income or capital gain, except when your investment is through an IRA, 401(k) or other tax-advantaged account.

Payments to broker/dealers and other financial intermediaries

The fund’s related companies may pay broker/dealers or other financial intermediaries (such as a bank or an insurance company) for the sale of fund shares and related services. These payments create a conflict of interest by influencing your broker/dealer or other intermediary or its employees or associated persons to recommend the fund over another investment. Ask your financial adviser or salesperson or visit your financial intermediary’s or salesperson’s website for more information.

Legg Mason Target Retirement 2030

Investment objectives

The fund seeks the highest total return (that is, a combination of income and long-term capital appreciation) over time consistent with its asset mix. From the five years before until the five years after the fund’s target retirement date of 2030 (the “Dynamic Rebalancing Period”), the fund will seek to reduce volatility as a secondary objective.

Fees and expenses of the fund

The accompanying table describes the fees and expenses that you may pay if you buy and hold shares of the fund.

You may qualify for sales charge discounts if you and your family invest, or agree to invest in the future, at least $25,000 in funds sold by Legg Mason Investor Services, LLC (“LMIS”), the fund’s distributor. More information about these and other discounts is available from your financial intermediary, in this Prospectus on page 126 under the heading “Sales charges” and in the fund’s statement of additional information (“SAI”) on page 89 under the heading “Sales Charge Waivers and Reductions.”

The fund no longer offers Class R1 shares for purchase by new or existing investors.

Example

This example is intended to help you compare the cost of investing in the fund with the cost of investing in other mutual funds. The example assumes:

Fees and expenses of the fund cont’d

Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Portfolio turnover. The fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the fund’s performance. During the most recent fiscal year, the fund’s portfolio turnover rate was 49% of the average value of its portfolio.

Principal investment strategies

The fund is a fund of funds—it invests primarily in other funds. These underlying funds are open-end funds managed by the manager or its affiliates, or exchange-traded funds (“ETFs”) that are based on an index and managed by unaffiliated investment advisers.

The fund seeks to achieve its objectives by investing in a combination of underlying funds representing a variety of broad asset classes—equity, fixed income and inflation-hedging—and investment styles. The fund is designed for investors expecting to retire around 2030. The fund’s asset mix has been designed on the expectation that investors will begin to withdraw assets from the fund during 2030, but will continue to maintain a significant portion of their investment in the fund for a period of time—perhaps 10 to 20 years—following that date. While the fund seeks to reduce volatility during the Dynamic Rebalancing Period, the fund may not achieve its goals. You should take these factors into consideration when deciding on an investment in the fund.

The fund generally seeks to maintain a certain Target Allocation, as described below. However, during the Dynamic Rebalancing Period, Legg Mason Global Asset Allocation, LLC (“LMGAA”), one of the fund’s subadvisers, in its discretion, may adjust the fund’s asset mix as often as daily and may vary the fund’s allocation substantially from the Target Allocation. The fund’s Target Allocation for equity funds (including real estate-related funds), fixed income funds and inflation-hedging funds is shown in the table below:

LMGAA is responsible for implementation of the fund’s overall asset allocation. During the fund’s Dynamic Rebalancing Period, LMGAA also manages the assets allocated to the Dynamic Risk Management strategy. Western Asset Management Company (“Western Asset”), the fund’s other subadviser, manages the assets

allocated to the Event Risk Management strategy, described below, during the fund’s Dynamic Rebalancing Period.

Glide path period

Over time, the allocation to asset classes and underlying funds will change according to a predetermined “glide path.” The glide path represents the shifting of asset classes over time. The glide path is detailed in the chart below:

During the time that the fund’s asset allocations track the glide path, the fund’s asset mix will gradually become more conservative until approximately 2045, or 15 years after the target date, at which time the asset mix will become static. This reflects the goal of pursuing the highest total return, consistent with a reasonable amount of risk, during the investor’s pre-retirement and early retirement years. By following these investment strategies after the fund reaches its target date, the fund seeks to reduce the likelihood that an investor will experience a significant loss of capital at a more advanced age.

The Target Allocations reflected in the glide path are “neutral” allocations, which do not reflect tactical decisions made by LMGAA to overweight or underweight a particular asset class. From time to time, LMGAA may make tactical increases or decreases to the fund’s investment in a particular asset class beyond the Target Allocation, based on a broad range of market and economic trends and quantitative factors. LMGAA may also allow the relative weightings of the fund’s investments in asset classes to vary from its Target Allocation in response to the markets.

Dynamic rebalancing period

During the Dynamic Rebalancing Period, the fund will not be managed strictly according to the standard Target Allocation. Instead, LMGAA will implement a combination of risk management strategies that will attempt to limit downside volatility within the fund. These strategies include Dynamic Risk Management and Event Risk Management, as described below. Through both strategies, the fund gives up some of the potential for high total return that could be achieved if the fund were to follow its Target Allocation under positive market conditions. In exchange, these strategies are intended to result in less significant declines in the fund’s net asset value (“NAV”) under negative market conditions. The fund’s NAV will fluctuate and is not guaranteed.

Dynamic risk management. The Dynamic Risk Management strategy will seek to reduce the fund’s market risk exposure and volatility. As frequently as daily, the Dynamic Risk Management strategy may increase the fund’s exposure to short-term defensive instruments (including Treasury bills, money market funds and cash) in response to certain levels of negative fund performance. At other times Dynamic Risk Management may decrease the fund’s exposure to short-term defensive instruments and increase its exposure to equity funds and long-term fixed income funds in order to return to the fund’s Target Allocation in response to certain levels of positive fund performance. The maximum daily allocation to short-term defensive instruments will be 95% of the fund’s net assets.

Principal investment strategies cont’d

In response to certain levels of negative fund performance, LMGAA may increase the fund’s exposure to short-term defensive instruments (“de-risking”) based on a formula that takes into account the fund’s current NAV, macro-economic conditions, and the fund’s underlying volatility. In order to implement this strategy, LMGAA anticipates that it will initially attempt to sell shares of ETFs and other liquid securities or engage in short sale transactions involving futures. Then, LMGAA would redeem underlying open-end mutual fund shares as needed. In response to certain levels of positive fund performance, the fund may purchase ETFs or underlying open-end mutual fund shares or cover short futures positions (when the fund is not managed strictly according to the standard Target Allocation). LMGAA, in its discretion, will determine the levels and timing for Dynamic Risk Management. If LMGAA determines that de-risking is no longer appropriate, the fund will reverse this process, sell short-term defensive instruments and purchase equity funds and long-term fixed income funds in accordance with the fund’s Target Allocation.

LMGAA may from time to time make tactical increases or decreases to the fund’s investment in a particular asset class beyond the Target Allocation based on a broad range of market and economic trends and quantitative factors. LMGAA may also allow the relative weightings of the fund’s investments in asset classes to vary from its Target Allocation in response to the markets. When varying exposures among underlying funds, LMGAA will examine relative values and prospects among the underlying funds’ asset classes, as well as the capacity of the underlying funds to absorb additional cash flow.

Event risk management. The Event Risk Management strategy will seek to reduce the impact to the fund of market declines during a short period of time caused by, for example, sudden and substantial movements in the equity markets, interest rates or credit spreads. The fund initially will invest up to 2% of its net assets in this strategy (as measured by the premiums paid on options or initial margin on futures contracts). However, the fund may invest up to 7% of its net assets at the time of purchase in this strategy (as measured by the premiums paid on options or initial margin on futures contracts). If the fund’s holdings in this strategy increase in value to over 7% of its net assets as a result of market movements, the fund will reduce, at least monthly, the amount of its assets invested in this strategy to no more than 7% of its net assets. The value of the fund’s assets invested in this strategy may be substantially higher than the value of the premiums paid or initial margin amounts on the instruments used to implement the strategy. If the value of the instruments in the Event Risk Management strategy declines after the fund has engaged in “de-risking,” the fund’s NAV could decline even if the broader markets rise in value. Conversely, if the value of the instruments in the Event Risk Management strategy increases after the fund has engaged in “de-risking,” the fund’s net asset value could increase even if the broader markets fall in value.

Western Asset’s views and outlook regarding potential unexpected market movements will determine the investments and strategies it employs in implementing the Event Risk Management strategy. During normal market conditions, the fund will implement the Event Risk Management strategy through investments in options, futures, swaps or other instruments. Since the Event Risk Management strategy seeks to primarily benefit from large and unexpected market movements, there may be times when the investment and transaction costs related to hedging will result in losses to the fund. The Event Risk Management strategy will be actively managed in an effort to reduce these costs when possible.

Static allocation period

The fund’s Target Allocation will become static 15 years after the target date. At this time, when the fund’s Target Allocation will match the Target Allocation of Legg Mason Target Retirement Fund (the “Retirement Fund”), the fund’s Board of Trustees may combine the fund with the Retirement Fund without shareholder approval, and the fund’s shareholders will become shareholders of the Retirement Fund. This is expected to occur approximately in the year 2045. This combination is expected to be tax-free under current law. Shareholders will be provided with additional information at that time.

The Retirement Fund’s Target Allocation is 33% in equity, 62% in fixed income and 5% in inflation-hedging funds.

Certain risks

Risk is inherent in all investing. There is no assurance that the fund will meet its investment objectives. The value of your investment in the fund, as well as the amount of return you receive on your investment, may fluctuate significantly. You may lose part or all of your investment in the fund or your investment may not perform as well as other similar investments. In addition, you may experience losses

near, at or after the target date. You should not rely solely on the target date when choosing to invest in the fund or deciding to remain invested in the fund. You should consider the fund’s investment strategies over the whole life of the fund. Unlike many other target retirement date funds, the fund, during the Dynamic Rebalancing Period, may not follow the Target Allocation indicated by the glide path. There is no assurance that the fund will provide sufficient retirement income at and after the target date. The following is a summary description of certain risks of investing in the fund.

Affiliated funds risk. The fund’s manager serves as manager of certain underlying funds and is affiliated with the manager of other underlying funds. In addition, the fund may invest in certain underlying funds for which LMGAA or Western Asset serve as adviser. It is possible that a conflict of interest among the fund and the underlying funds could affect how the fund’s manager, LMGAA or Western Asset fulfill their fiduciary duties to the fund and the underlying funds. For example, LMGAA may have an incentive to allocate the fund’s assets or to maintain the fund’s allocation to those funds for which the fees paid to the manager or a subadviser are higher than the fees paid by other underlying funds or to those funds for which a subadviser serves as adviser. However, the fund has adopted procedures to mitigate these concerns.

In order to implement the Dynamic Risk Management strategy, LMGAA anticipates that it will initially sell shares the fund holds in ETFs and other liquid securities or engage in short sale transactions involving index options and index futures contracts.

Then, LMGAA would redeem shares of underlying open-end mutual funds as needed. As a result, there may be conflicts of interest if unaffiliated ETFs are sold before affiliated underlying open-end mutual funds.

Allocation risk. The fund’s ability to achieve its investment objectives depends upon LMGAA’s skill in determining the fund’s asset class allocation, creating and applying formulas for de-risking or ending de-risking, determining when to engage in Event Risk Management and in selecting the best mix of underlying funds. The value of your investment may decrease if LMGAA’s judgment about the attractiveness, value or market trends affecting a particular asset class, investment style, technique or strategy, underlying fund or other issuer is incorrect.

In implementing the Dynamic Risk Management or Event Risk Management strategies, the fund will be subject to heightened allocation risk, as LMGAA will have discretion in determining the fund’s asset class allocation. If the fund increases its exposure to short-term defensive instruments at inopportune times or for extended periods of time, the fund may experience lower performance and greater losses.

Cash management and defensive investing risk. During the Dynamic Rebalancing Period, the fund may have significant exposure to short-term defensive instruments, which typically will include Treasury bills, money market funds and cash. The fund may also engage in short sale transactions involving index options and index futures contracts. The value of these investments held by the fund can fluctuate. Like other fixed income securities, they are subject to risk, including market, interest rate and credit risk. If the fund holds cash uninvested, it will be subject to the credit risk of the depository institution holding the cash. If the fund holds cash uninvested, the fund will not earn income on the cash. If the fund has a significant amount of exposure to short-term defensive instruments or the fund sells index options or index futures contracts short, it may not achieve high total returns.

Derivatives risk. Using derivatives may have a leveraging effect, which may result in a disproportionate increase in fund losses on the investment, and reduce opportunities for gains when market prices, interest rates or the derivative instruments themselves behave in a way not anticipated by the fund. Using derivatives also can increase fund volatility. Derivatives may be difficult to sell, unwind or value, and the counterparty may default on its obligations to the fund. Recent legislation calls for new regulation of the derivatives markets. The extent and impact of the regulation are not yet fully known and may not be for some time. New regulation of derivatives may make them more costly, may limit their availability, or may otherwise adversely affect their value or performance. Derivatives used for hedging purposes may have an imperfect correlation to the assets held by the fund and may not adequately protect against losses in or may result in greater losses for the fund’s portfolio.

Dynamic risk management strategy risk. In implementing the Dynamic Risk Management strategy, LMGAA anticipates that it will initially sell shares the fund holds in ETFs and other liquid securities or engage in short sale transactions involving index options and index futures contracts. Then, LMGAA would redeem shares of underlying open-end mutual funds as needed. As a result, the fund’s assets may be more concentrated in its

Certain risks cont’d

underlying mutual fund holdings. In addition, during periods of market volatility, the share prices of ETFs may deviate significantly from their NAVs. Therefore, selling shares of ETFs during periods of market volatility may result in greater losses than redeeming open-end mutual fund holdings. Similarly, the use of derivatives may cause the fund to experience greater losses than redeeming mutual fund holdings. The fund may incur additional trading costs while implementing the Dynamic Risk Management strategy, which may reduce the fund’s performance. There is no guarantee that the Dynamic Risk Management strategy will work and shareholders should evaluate their ability to invest for the long-term, especially during periods of downturn in the market.

Event risk management strategy risk. The Event Risk Management strategy may involve entering into transactions involving options, futures and swaps that are expected to increase in value during the occurrence of certain market events. An instrument used to hedge market event risk could lose all or a portion of its value even in a period of severe market stress. Implementation of the strategy may result in the fund holding options and futures positions that take contradictory views on market movements. The costs of purchasing and selling these instruments may reduce the fund’s return. The fund may not be able to close out a position at the desired time or price. There is no guarantee that the Event Risk Management strategy will work and shareholders should evaluate their ability to invest for the long term, especially during periods of downturn in the market.

Tax risk. The fund’s hedging strategy may result in the fund deferring, possibly indefinitely, certain of its realized losses for U.S. federal income tax purposes, potentially increasing the amount of the fund’s taxable distributions paid to shareholders.

Short sales risk. A short sale of a security involves the risk that instead of declining, the price of the security sold short will rise. If the price of the security sold short increases between the time of the short sale and the time the fund replaces the borrowed security, the fund will realize a loss. The short sale of securities involves the possibility of a theoretically unlimited loss since there is a theoretically unlimited potential for the market price of the security sold short to increase. Shorting futures may have an imperfect correlation to the assets held by the fund and may not adequately protect against losses in or may result in greater losses for the fund’s portfolio.

Segregated assets risk. In connection with certain transactions that may give rise to future payment obligations, including many types of derivatives, the fund may be required to maintain a segregated amount of cash or liquid securities to cover the position. Segregated securities cannot be sold while the position they are covering is outstanding, unless they are replaced with other securities of equal value. As a result, there is the possibility that segregation of a large percentage of the fund’s assets, in some circumstances, may limit the subadvisers’ flexibility.

Asset class variation risk. The underlying funds invest principally in the securities constituting their asset class ( i.e. , equity, fixed income, inflation-hedging investments and short-term defensive instruments). However, under normal market conditions, an underlying fund may vary the percentage of its assets in these securities (subject to any applicable regulatory requirements). Depending upon the percentage of securities in a particular asset class held by the underlying funds at any given time and the percentage of the fund’s assets invested in various underlying funds, the fund’s actual exposure to the securities in a particular asset class may vary substantially from its Target Allocation for that asset class.

Fund of funds risk. Your cost of investing in the fund, as a fund of funds, may be higher than the cost of investing in a mutual fund that only invests directly in individual securities. An underlying fund may change its investment objective or policies without the fund’s approval, which could force the fund to withdraw its investment from such underlying fund at a time that is unfavorable to the fund. In addition, one underlying fund may buy the same securities that another underlying fund sells. Therefore, the fund would indirectly bear the costs of these trades without accomplishing any investment purpose.

Stock market and equity securities risk. The securities markets are volatile and the market prices of the fund’s or underlying fund’s securities may decline generally. Securities fluctuate in price based on changes in a company’s financial condition and overall market and economic conditions. If the market prices of the securities owned by the fund or underlying fund fall, the value of your investment in the fund will decline. The financial crisis that began in 2008 has caused a significant decline in the value and liquidity of many securities of issuers worldwide. In response to the crisis, the U.S. and other governments and the Federal Reserve and certain foreign central banks have taken steps to support

financial markets. These market conditions may continue, worsen or spread, including in the United States, Europe and beyond. The withdrawal of this support, failure of efforts to respond to the crisis, or investor perception that such efforts are not succeeding could also negatively affect financial markets generally as well as the value and liquidity of certain securities. Whether or not the fund or underlying fund invests in securities of issuers located in or with significant exposure to countries experiencing economic and financial difficulties, the value and liquidity of the fund’s or underlying fund’s investments may be negatively affected by the conditions in the countries experiencing the difficulties. In addition, policy and legislative changes in the United States and in other countries are changing many aspects of financial regulation. The impact of these changes on the markets, and the practical implications for market participants, may not be fully known for some time.

Fixed income securities risk. Fixed income securities are subject to a number of risks, including credit, market and interest rate risks. Credit risk is the risk that the issuer or obligor will not make timely payments of principal and interest. Changes in an issuer’s credit rating or the market’s perception of an issuer’s creditworthiness may also affect the value of an underlying fund’s investment in that issuer. Market risk is the risk that the fixed income markets may become volatile and less liquid, and the market value of an investment may move up or down, sometimes quickly or unpredictably. Interest rate risk is the risk that the value of a fixed income security will fall when interest rates rise. In general, the longer the maturity and the lower the credit quality of a fixed income security, the more likely its value will decline.

Issuer risk. The value of a security can go up or down more than the market as a whole and can perform differently from the value of the market as a whole, often due to disappointing earnings reports by the issuer, unsuccessful products or services, loss of major customers, major litigation against the issuer or changes in government regulations affecting the issuer or the competitive environment. An underlying fund may experience a substantial or complete loss on an individual security. Historically, the prices of securities of small and medium capitalization companies have generally gone up or down more than those of large capitalization companies, although even large capitalization companies may fall out of favor with investors.

Large capitalization company risk. Large capitalization companies may fall out of favor with investors.

Small and medium capitalization company risk. An underlying fund will be exposed to additional risks as a result of its investments in the securities of small and medium capitalization companies. Small and medium capitalization companies may fall out of favor with investors; may have limited product lines, operating histories, markets or financial resources; or may be dependent upon a limited management group. The prices of securities of small and medium capitalization companies generally are more volatile than those of large capitalization companies and are more likely to be adversely affected than large capitalization companies by changes in earnings results and investor expectations or poor economic or market conditions, including those experienced during a recession. Securities of small and medium capitalization companies may underperform large capitalization companies, may be harder to sell at times and at prices an underlying fund’s adviser believes appropriate and may offer greater potential for losses.

Liquidity risk. Some assets or derivatives held by the fund or an underlying fund or futures sold by the fund or an underlying fund may be difficult to sell, or illiquid, particularly during times of market turmoil. Illiquid assets or derivatives may also be difficult to value. If the fund or an underlying fund is forced to sell an illiquid asset to meet redemption requests or other cash needs, the fund or an underlying fund may be forced to sell at a loss.

Growth and value investing risk. Growth or value securities as a group may be out of favor and underperform the overall equity market while the market concentrates on other types of securities. Growth securities typically are very sensitive to market movements because their market prices tend to reflect future expectations. When it appears those expectations will not be met, the prices of growth securities typically fall. The value approach to investing involves the risk that stocks may remain undervalued. An underlying fund may, like many growth or value funds, weight its investments toward certain industries, thus increasing its exposure to factors adversely affecting issuers within those industries and, indirectly, the fund’s exposure to those factors.

Foreign investment risk. The fund or an underlying fund’s investments in securities of foreign issuers or issuers with significant exposure to foreign markets involve additional risk. Foreign countries in which

Certain risks cont’d

the fund or an underlying fund may invest may have markets that are less liquid, less regulated and more volatile than U.S. markets. The value of the fund or an underlying fund’s investments may decline because of factors affecting the particular issuer as well as foreign markets and issuers generally, such as unfavorable government actions, and political or financial instability. Lack of information may also affect the value of these securities.

The risks of foreign investments are heightened when investing in issuers in emerging market countries.

Currency risk. The value of investments in securities denominated in foreign currencies increases or decreases as the rates of exchange between those currencies and the U.S. dollar change. Currency conversion costs and currency fluctuations could erase investment gains or add to investment losses. Currency exchange rates can be volatile, and are affected by factors such as general economic conditions, the actions of the U.S. and foreign governments or central banks, the imposition of currency controls and speculation.

Real estate investment trusts (REITs) risk. Investments in REITs expose an underlying fund to risks similar to investing directly in real estate, such as changes in the value of the underlying real estate, the quality of the property management, the creditworthiness of the issuer of the investments, and changes in property taxes, interest rates and the real estate regulatory environment.

Exchange-traded funds (ETFs) risk. Investing in an ETF will give the fund exposure to the securities comprising the index on which the ETF is based and will expose the fund to risks similar to those of investing directly in those securities. Shares of ETFs are traded on an exchange and may trade at either a premium or discount to NAV. The fund will pay brokerage commissions in connection with the purchase and sale of shares of ETFs.

Valuation risk. The sales price the fund or an underlying fund could receive for any particular portfolio investment may differ from the fund’s valuation of the investment, particularly for securities or other instruments that trade in thin or volatile markets or that are valued using a fair value methodology. Investors who purchase or redeem fund shares on days when the fund or an underlying fund is holding fair-valued securities may receive fewer or more shares or lower or higher redemption proceeds than they would have received if the fund or the underlying fund had not fair-valued the security or had used a different valuation methodology.

Risk of increase in expenses. Your actual costs of investing in the fund may be higher than the expenses shown in “Annual fund operating expenses” for a variety of reasons. For example, expense ratios may be higher than those shown if a fee limitation is changed or terminated or if average net assets decrease. Net assets are more likely to decrease and fund expense ratios are more likely to increase when markets are volatile. In addition, after the fund reaches the target date, it is expected that the assets will decline as investors begin to withdraw their assets from the fund, causing gross expenses to increase.