Summary Prospectus by Investment Company (Form 497K)

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BlackRock Retirement Income 2040 Fund

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A contingent deferred sales charge ("CDSC") of 1.00% is assessed on certain redemptions of Investor A Shares made within 18 months after purchase where no initial sales charge was paid at the time of purchase as part of an investment of $1,000,000 or more.

2

BlackRock has contractually agreed to waive its management fees by the amount of investment advisory fees the Fund pays to BlackRock indirectly through its investment in money market funds managed by BlackRock or its affiliates, through June 30, 2026. The contractual agreements may be terminated upon 90 days' notice by a majority of the non-interested trustees of BlackRock Funds II or by a vote of a majority of the outstanding voting securities of the Fund.

3

Total Annual Fund Operating Expenses do not correlate to the ratios of expenses to average net assets given in the Fund's most recent annual financial statements and additional information, which do not include Acquired Fund Fees and Expenses.

4

As described in the "Management of the Funds" section of the Fund's prospectus beginning on page 62, BlackRock has contractually agreed to waive and/or reimburse fees or expenses in order to limit Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements (excluding Dividend Expense, Interest Expense, Acquired Fund Fees and Expenses and certain other Fund expenses) to 0.50% (for Investor A Shares) and 0.25% (for Institutional Shares) of average daily net assets through June 30, 2026. The Fund may have to repay some of these waivers and/or reimbursements to BlackRock in the two years following such waivers and/or reimbursements. Any such repayment obligation will terminate on July 31, 2027. The contractual agreement may be terminated upon 90 days' notice by a majority of the non-interested trustees of the Trust or by a vote of a majority of the outstanding voting securities of the Fund.

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Affiliated Fund Risk - In managing the Fund, BlackRock will have authority to allocate to the Underlying Fund as it deems appropriate, based on the Fund's investment objective and investment strategies. BlackRock may be subject to conflicts of interest in selecting the Underlying Fund because the fees paid to BlackRock by the Underlying Fund may be higher than the fees paid by other underlying funds. However, BlackRock is a fiduciary to the Fund and is legally obligated to act in the Fund's best interests when allocating its assets.

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Managed Distribution Tax Risk - The Fund uses a proprietary Algorithm to seek to maximize monthly distributions while decumulating the Fund's assets to a Target Percentage over the term of the Fund. To achieve decumulation and to maintain monthly distributions, subject to an Annual Minimum Distribution Amount, the Fund may be required to dispose of investments. The Fund's disposition of investments could accelerate the timing of the Fund's recognition of taxable income and capital gains and cause the Fund to make taxable distributions earlier than the Fund otherwise would have. In addition, to achieve decumulation and to maintain monthly distributions, subject to an Annual Minimum Distribution Amount, the Fund's distributions will generally exceed the Fund's income and gains for the Fund's taxable year. Distributions in excess of the Fund's current and accumulated earnings and profits will be treated as a return of capital. In general, a return of capital is not immediately taxable to a shareholder. Rather,

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Model Risk - The Fund seeks to pursue its investment objective by using the Algorithm, which is designed to maximize monthly distributions, subject to an Annual Minimum Distribution Amount, while decumulating the Fund's assets to a Target Percentage, over the term of the Fund. The ability of the Fund to make such distributions, subject to an Annual Minimum Distribution Amount, and to achieve the Target Percentage may differ from what is forecasted in the Algorithm due to the factors incorporated into the Algorithm and the weighting of each factor, as well as the level and scope of changes from historical trends. In addition, issues in the construction and implementation of the Algorithm, including software or hardware malfunction, power loss, software bugs, malicious code, viruses, system crashes and other technological failures or various other events or circumstances within or beyond the control of BlackRock, may adversely impact the Fund. There is no guarantee that BlackRock's use of the Algorithm will be effective in helping the Fund seek to achieve its investment objective.

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Limited Term Risk - The Fund's limited term may cause it to sell securities when it otherwise would not, including at times when market conditions are not favorable, or otherwise in severe distress, which could cause the Fund's returns to decrease and the net asset value of its shares to fall. In addition, during the life of the Fund, the value of the Fund's assets could change significantly, and the Fund could incur substantial losses prior to or at liquidation. Although the Fund seeks to decumulate the Fund's assets to a Target Percentage over the term of the Fund, the Fund may not be successful in achieving this objective. The return of the Target Percentage is not an express or implied obligation of the Fund. There can be no assurance that the Fund will be able to return any specific Target Percentage, and such return is not backed or otherwise guaranteed by BlackRock or any other entity. Depending upon a variety of factors, including the performance of the Fund's portfolio over the life of the Fund and the Fund's intention to provide monthly distributions, subject to an Annual Minimum Distribution Amount, during the term that may include return of capital, the amount distributed to shareholders at liquidation may be significantly less than the Target Percentage. The Fund's ability to return the Target Percentage at liquidation will depend on market conditions, the performance of the Fund's portfolio investments and cash flow management. The Fund may set aside a portion of its net investment income, and possibly all or a portion of its gains, in pursuit of its objective to return the Target Percentage to shareholders upon liquidation; provided, however, that the Fund will distribute at least enough net investment income for the Fund to satisfy the 90% annual distribution requirement applicable to regulated investment companies. This will reduce the amounts otherwise available for distribution prior to liquidation as well as the Fund's distributions during the period prior to liquidation. There can be no assurance that the Fund will be able to make a distribution in any particular month over the term of the Fund. There is no guarantee that the Fund will distribute the Annual Minimum Distribution Amount in any given year.

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Allocation Risk - There is no guarantee that the Underlying Fund will achieve its investment objective, and the Underlying Fund's performance may be lower than the performance of the asset class which it was selected to represent. The Underlying Fund may change its investment objective or policies without the approval of the Fund. If the Underlying Fund were to change its investment objective or policies, the Fund might be forced to withdraw its investment from the Underlying Fund at a disadvantageous time and price.

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Collateralized Debt Obligations Risk - In addition to the typical risks associated with fixed-income securities and asset-backed securities, collateralized debt obligations ("CDOs"), including collateralized loan obligations, carry additional risks including, but not limited to: (i) the possibility that distributions from collateral securities will not be adequate to make interest or other payments; (ii) the risk that the collateral may default or decline in value or be downgraded, if rated by a nationally recognized statistical rating organization; (iii) the Fund may invest in tranches of CDOs that are subordinate to other tranches; (iv) the structure and complexity of the transaction and the legal documents could lead to disputes among investors regarding the characterization of proceeds; (v) the investment return achieved by the Fund could be significantly different than those predicted by financial models; (vi) the lack of a readily available secondary market for CDOs; (vii) the risk of forced "fire sale" liquidation due to technical defaults such as coverage test failures; and (viii) the CDO's manager may perform poorly.

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Convertible Securities Risk - The market value of a convertible security performs like that of a regular debt security; that is, if market interest rates rise, the value of a convertible security usually falls. In addition, convertible securities are subject to the risk that the issuer will not be able to pay interest, principal or dividends when due, and their market value may change based on changes in the issuer's credit rating or the market's perception of the issuer's creditworthiness. Since it derives a portion of its value from the common stock into which it may be converted, a convertible security is also subject to the same types of market and issuer risks that apply to the underlying common stock, including the potential for increased volatility in the price of the convertible security.

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Corporate Loans Risk - Commercial banks and other financial institutions or institutional investors make corporate loans to companies that need capital to grow or restructure. Borrowers generally pay interest on corporate loans at rates that change in response to changes in market interest rates such as the Secured Overnight Financing Rate ("SOFR") or the prime rates of U.S. banks. As a result, the value of corporate loan investments is generally less exposed to the adverse effects of shifts in market interest rates than investments that pay a fixed rate of interest.

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Counterparty Risk - The counterparty to an over-the-counter derivatives contract or a borrower of the Fund's securities may be unable or unwilling to make timely principal, interest or settlement payments, or otherwise to honor its obligations. Any such failure to honor its obligations may cause significant losses to the Fund.

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Covered Call Risk - The Fund intends to invest in covered call options and structured notes that provide exposure to covered call options. Covered call risk is the risk that the issuer of the call option will forgo any profit from increases in the market value of the underlying security covering the call option above the sum of the premium and the strike price of the call but retain the risk of loss if the underlying security declines in value. The Fund will have no control over the exercise of the option by the option holder and may lose the benefit from any capital appreciation on the underlying security. A number of factors may influence the option holder's decision to exercise the option, including the value of the underlying security, price volatility, dividend yield and interest rates. To the extent that these factors increase the value of the call option, the option holder is more likely to exercise the option, which may negatively affect the Fund.

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Debt Securities Risk - Debt securities, such as bonds, involve risks, such as credit risk, interest rate risk, extension risk, and prepayment risk, each of which are described in further detail below:

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Derivatives Risk - The Fund's use of derivatives may increase its costs, reduce the Fund's returns and/or increase volatility. Derivatives involve significant risks, including:

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Distressed Securities Risk - Distressed securities are speculative and involve substantial risks in addition to the risks of investing in junk bonds. The Fund will generally not receive interest payments on the distressed securities and may incur costs to protect its investment. In addition, distressed securities involve the substantial risk that principal will not be repaid. These securities may present a substantial risk of default or may be in default at the time of investment. The Fund may incur additional expenses to the extent it is required to seek recovery upon a default in the payment of principal of or interest on its portfolio holdings. In any reorganization or liquidation proceeding relating to a portfolio company, the Fund may lose its entire investment or may be required to accept

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Dollar Rolls Risk - Dollar rolls involve the risk that the market value of the securities that the Fund is committed to buy may decline below the price of the securities the Fund has sold. These transactions may involve leverage.

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Emerging Markets Risk - Emerging markets are riskier than more developed markets because they tend to develop unevenly and may never fully develop. Investments in emerging markets may be considered speculative. Emerging markets are more likely to experience hyperinflation and currency devaluations, which adversely affect returns to U.S. investors. In addition, many emerging securities markets have far lower trading volumes and less liquidity than developed markets.

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Equity Securities Risk - Stock markets are volatile. The price of equity securities fluctuates based on changes in a company's financial condition and overall market and economic conditions.

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Foreign Securities Risk - Foreign investments often involve special risks not present in U.S. investments that can increase the chances that the Fund will lose money. These risks include:

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The Fund generally holds its foreign securities and cash in foreign banks and securities depositories, which may be recently organized or new to the foreign custody business and may be subject to only limited or no regulatory oversight.

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Changes in foreign currency exchange rates can affect the value of the Fund's portfolio.

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The economies of certain foreign markets may not compare favorably with the economy of the United States with respect to such issues as growth of gross national product, reinvestment of capital, resources and balance of payments position.

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The governments of certain countries, or the U.S. Government with respect to certain countries, may prohibit or impose substantial restrictions through capital controls and/or sanctions on foreign investments in the capital markets or certain industries in those countries, which may prohibit or restrict the ability to own or transfer currency, securities, derivatives or other assets.

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Many foreign governments do not supervise and regulate stock exchanges, brokers and the sale of securities to the same extent as does the United States and may not have laws to protect investors that are comparable to U.S. securities laws.

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Settlement and clearance procedures in certain foreign markets may result in delays in payment for or delivery of securities not typically associated with settlement and clearance of U.S. investments.

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The Fund's claims to recover foreign withholding taxes may not be successful, and if the likelihood of recovery of foreign withholding taxes materially decreases, due to, for example, a change in tax regulation or approach in the foreign country, accruals in the Fund's net asset value for such refunds may be written down partially or in full, which will adversely affect the Fund's net asset value.

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The European financial markets have recently experienced volatility and adverse trends due to concerns about economic downturns in, or rising government debt levels of, several European countries as well as acts of war in the region. These events may spread to other countries in Europe and may affect the value and liquidity of certain of the Fund's investments.

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High Yield Bonds Risk - Although junk bonds generally pay higher rates of interest than investment grade bonds, junk bonds are high risk investments that are considered speculative and may cause income and principal losses for the Fund.

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Illiquid Investments Risk - The Fund may not acquire any illiquid investment if, immediately after the acquisition, the Fund would have invested more than 15% of its net assets in illiquid investments. An illiquid investment is any investment that the Fund reasonably expects cannot be sold or disposed of in current market conditions in seven calendar days or less without the sale or disposition significantly changing the market value of the investment. Liquid investments may become illiquid after purchase by the Fund, particularly during periods of market turmoil. There can be no assurance that a security or instrument that is deemed to be liquid when purchased will continue to be liquid for as long as it is held by the Fund, and any security or instrument held by the Fund may be deemed an illiquid investment pursuant to the Fund's liquidity risk management program. The Fund's illiquid investments may reduce the returns of the Fund because it may be difficult to sell the illiquid investments at an advantageous time or price. In addition, if the Fund is limited in its ability to sell illiquid investments during periods when shareholders are redeeming their shares, the Fund will need to sell liquid securities to meet redemption requests and illiquid securities will become a larger portion of the Fund's holdings. An investment may be illiquid due to, among other things, the reduced number and capacity of traditional market participants to make a market in fixed-income securities or the lack of an active trading market. To the extent that the Fund's principal investment strategies involve derivatives or securities with substantial market and/or credit risk, the Fund will tend to have the greatest

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Indexed Securities Risk - Indexed securities provide a potential return based on a particular index of value or interest rates. The Fund's return on these securities will be subject to risk with respect to the value of the particular index. These securities are subject to leverage risk and correlation risk. Certain indexed securities have greater sensitivity to changes in interest rates or index levels than other securities, and the Fund's investment in such instruments may decline significantly in value if interest rates or index levels move in a way Fund management does not anticipate.

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Investment in Other Investment Companies Risk - As with other investments, investments in other investment companies, including exchange-traded funds, are subject to market and selection risk. In addition, if the Fund acquires shares of investment companies, including ones affiliated with the Fund, shareholders bear both their proportionate share of expenses in the Fund (including management and advisory fees) and, indirectly, the expenses of the investment companies (to the extent not offset by BlackRock through waivers). To the extent the Fund is held by an affiliated fund, the ability of the Fund itself to hold other investment companies may be limited.

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Leverage Risk - Some transactions may give rise to a form of economic leverage. These transactions may include, among others, derivatives, and may expose the Fund to greater risk and increase its costs. The use of leverage may cause the Fund to liquidate portfolio positions when it may not be advantageous to do so to satisfy its obligations or to meet the applicable requirements of the Investment Company Act of 1940, as amended (the "Investment Company Act"), and the rules thereunder. Increases and decreases in the value of the Fund's portfolio will be magnified when the Fund uses leverage.

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Market Risk and Selection Risk - Market risk is the risk that one or more markets in which the Fund invests will go down in value, including the possibility that the markets will go down sharply and unpredictably. The value of a security or other asset may decline due to changes in general market conditions, economic trends or events that are not specifically related to the issuer of the security or other asset, or factors that affect a particular issuer or issuers, exchange, country, group of countries, region, market, industry, group of industries, sector or asset class. Local, regional or global events such as war, acts of terrorism, the spread of infectious illness or other public health issues like pandemics or epidemics, recessions, or other events could have a significant impact on the Fund and its investments. Selection risk is the risk that the securities selected by Fund management will underperform the markets, the relevant indices or the securities selected by other funds with similar investment objectives and investment strategies. The Fund seeks to pursue its investment objective by using the Algorithm that seeks to provide monthly distributions, subject to an Annual Minimum Distribution Amount, as well as decumulating assets to a Target Percentage, and is subject to "Model Risk" as described above. The Fund's Algorithm and limited term may cause it to sell its securities when it otherwise would not, including at times when market conditions are not favorable, or otherwise in severe distress, which could cause the Fund's returns to decrease and the net asset value of its shares to fall. This means you may lose money.

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Mortgage- and Asset-Backed Securities Risks - Mortgage- and asset-backed securities represent interests in "pools" of mortgages or other assets, including consumer loans or receivables held in trust. Mortgage- and asset-backed securities are subject to credit, interest rate, prepayment and extension risks. These securities also are subject to risk of default on the underlying mortgage or asset, particularly during periods of economic downturn. Small movements in interest rates (both increases and decreases) may quickly and significantly reduce the value of certain mortgage-backed securities.

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"New Issues" Risk - "New issues" are initial public offerings ("IPOs") of equity securities. Securities issued in IPOs have no trading history, and information about the companies may be available for very limited periods. In addition, the prices of securities sold in IPOs may be highly volatile or may decline shortly after the IPO.

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Preferred Securities Risk - Preferred securities may pay fixed or adjustable rates of return. Preferred securities are subject to issuer-specific and market risks applicable generally to equity securities. In addition, a company's preferred securities generally pay dividends only after the company makes required payments to holders of its bonds and other debt. For this reason, the value of preferred securities will usually react more strongly than bonds and other debt to actual or perceived changes in the company's financial condition or prospects. Preferred securities of smaller companies may be more vulnerable to adverse developments than preferred securities of larger companies.

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Reference Rate Replacement Risk - The Fund may be exposed to financial instruments that recently transitioned from, or continue to be tied to, LIBOR to determine payment obligations, financing terms, hedging strategies or investment value.

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REIT Investment Risk - Investments in REITs involve unique risks. REITs may have limited financial resources, may trade less frequently and in limited volume, may engage in dilutive offerings of securities and may be more volatile than other securities. REIT issuers may also fail to maintain their exemptions from investment company registration or fail to qualify for the "dividends paid deduction" under the Internal Revenue Code of 1986, as amended (the "Internal Revenue Code"), which allows REITs to reduce their corporate taxable income for dividends paid to their shareholders.

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Repurchase Agreements and Purchase and Sale Contracts Risk - If the other party to a repurchase agreement or purchase and sale contract defaults on its obligation under the agreement, the Fund may suffer delays and incur costs or lose money in exercising its rights under the agreement. If the seller fails to repurchase the security in either situation and the market value of the security declines, the Fund may lose money.

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Restricted Securities Risk - Limitations on the resale of restricted securities may have an adverse effect on their marketability, and may prevent the Fund from disposing of them promptly at advantageous prices. Restricted securities may not be listed on an exchange and may have no active trading market. In order to sell such securities, the Fund may have to bear the expense of registering the securities for resale and the risk of substantial delays in effecting the registration. Other transaction costs may be higher for restricted securities than unrestricted securities. Restricted securities may be difficult to value because market quotations may not be readily available, and the securities may have significant volatility. Also, the Fund may get only limited information about the issuer of a given restricted security, and therefore may be less able to predict a loss. Certain restricted securities may involve a high degree of business and financial risk and may result in substantial losses to the Fund.

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Risk of Investing in the United States - Certain changes in the U.S. economy, such as when the U.S. economy weakens or when its financial markets decline, may have an adverse effect on the securities to which the Fund has exposure.

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Structured Securities Risk - Because structured securities of the type in which the Fund may invest typically involve no credit enhancement, their credit risk generally will be equivalent to that of the underlying instruments, index or reference obligation and will also be subject to counterparty risk. The Fund may have the right to receive payments only from the structured security, and generally does not have direct rights against the issuer or the entity that sold the assets to be securitized. In addition to the general risks associated with debt securities discussed herein, structured securities carry additional risks, including, but not limited to: the possibility that distributions from collateral securities will not be adequate to make interest or other payments; the quality of the collateral may decline in value or default; and the possibility that the structured securities are subordinate to other classes. The Fund is permitted to invest in a class of structured securities that is either subordinated or unsubordinated to the right of payment of another class. Subordinated structured securities typically have higher yields and present greater risks than unsubordinated structured securities. Structured securities are typically sold in private placement transactions, and there currently is no active trading market for structured securities. Structured securities are based upon the movement of one or more factors, including currency exchange rates, interest rates, reference bonds and stock indices, and changes in interest rates and impact of these factors may cause significant price fluctuations. Additionally, changes in the reference instrument or security may cause the interest rate on the

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U.S. Government Issuer Risk - Treasury obligations may differ in their interest rates, maturities, times of issuance and other characteristics. Obligations of U.S. Government agencies and authorities are supported by varying degrees of credit but generally are not backed by the full faith and credit of the U.S. Government. No assurance can be given that the U.S. Government will provide financial support to its agencies and authorities if it is not obligated by law to do so.

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Variable and Floating Rate Instrument Risk - Variable and floating rate securities provide for periodic adjustment in the interest rate paid on the securities. Securities with floating or variable interest rates can be less sensitive to interest rate changes than securities with fixed interest rates, but may decline in value if their coupon rates do not reset as high, or as quickly, as comparable market interest rates, and generally carry lower yields than fixed securities of the same maturity. These securities will not generally increase in value if interest rates decline. A decline in interest rates may result in a reduction in income received from variable and floating rate securities held by the Fund and may adversely affect the value of the Fund's shares. These securities may be subject to greater illiquidity risk than other fixed income securities, meaning the absence of an active market for these securities could make it difficult for the Fund to dispose of them at any given time. Floating rate securities generally are subject to legal or contractual restrictions on resale, may trade infrequently, and their value may be impaired when the Fund needs to liquidate such loans. Benchmark interest rates may not accurately track market interest rates. Although floating rate securities are less sensitive to interest rate risk than fixed-rate securities, they are subject to credit risk and default risk, which could impair their value.