BlackRock Bond Fund, Inc.

BlackRock Total Return Fund

BlackRock Funds^SM

BlackRock Global Long/Short Credit Fund

BlackRock Impact Bond Fund

BlackRock Short Obligations Fund

BlackRock Short-Term Inflation-Protected Securities Index Fund

BlackRock Tactical Opportunities Fund

BlackRock Funds II

BlackRock 20/80 Target Allocation Fund

BlackRock 40/60 Target Allocation Fund

BlackRock 60/40 Target Allocation Fund

BlackRock 80/20 Target Allocation Fund

BlackRock Core Bond Portfolio

BlackRock Credit Strategies Income Fund

BlackRock Dynamic High Income Portfolio

BlackRock Emerging Markets Flexible Dynamic Bond Portfolio

BlackRock Floating Rate Income Portfolio

BlackRock Global Dividend Portfolio

BlackRock GNMA Portfolio

BlackRock High Yield Bond Portfolio

BlackRock Inflation Protected Bond Portfolio

BlackRock LifePath^® Smart Beta 2020 Fund

BlackRock LifePath^® Smart Beta 2025 Fund

BlackRock LifePath^® Smart Beta 2030 Fund

BlackRock LifePath^® Smart Beta 2035 Fund

BlackRock LifePath^® Smart Beta 2040 Fund

BlackRock LifePath^® Smart Beta 2045 Fund

BlackRock LifePath^® Smart Beta 2050 Fund

BlackRock LifePath^® Smart Beta 2055 Fund

BlackRock LifePath^® Smart Beta Retirement Fund

BlackRock Low Duration Bond Portfolio

BlackRock Managed Income Fund

BlackRock Multi-Asset Income Portfolio

BlackRock Strategic Income Opportunities Portfolio

BlackRock U.S. Government Bond Portfolio

BlackRock Funds III

BlackRock CoreAlpha Bond Fund

BlackRock LifePath^® Dynamic Retirement Fund

BlackRock LifePath^® Dynamic 2020 Fund

BlackRock LifePath^® Dynamic 2025 Fund

BlackRock LifePath^® Dynamic 2030 Fund

BlackRock LifePath^® Dynamic 2035 Fund

BlackRock LifePath^® Dynamic 2040 Fund

BlackRock LifePath^® Dynamic 2045 Fund

BlackRock LifePath^® Dynamic 2050 Fund

BlackRock LifePath^® Dynamic 2055 Fund

BlackRock LifePath^® Index Retirement Fund

BlackRock LifePath^® Index 2020 Fund

BlackRock LifePath^® Index 2025 Fund

BlackRock LifePath^® Index 2030 Fund

BlackRock LifePath^® Index 2035 Fund

BlackRock LifePath^® Index 2040 Fund

BlackRock LifePath^® Index 2045 Fund

BlackRock LifePath^® Index 2050 Fund

BlackRock LifePath^® Index 2055 Fund

BlackRock LifePath^® Index 2060 Fund

BlackRock U.S. Total Bond Index Fund

BlackRock Municipal Bond Fund, Inc.

BlackRock National Municipal Fund

BlackRock Short-Term Municipal Fund

BlackRock Strategic Global Bond Fund, Inc.

(each, a “Fund” and collectively, the “Funds”)

Supplement dated May 17, 2017 to the Statement of Additional Information (“SAI”) of each Fund

Effective June 5, 2017, each SAI is amended as follows:

The first paragraph in the section entitled “Shareholder Services—Exchange Privilege” in Part II of each Fund’s SAI is deleted in its entirety and replaced with the following:

U.S. shareholders of Investor A, Investor A1, Investor B, Investor B1, Investor C, Investor C1, Investor C2, Investor C3, Class K and Institutional Shares of each Fund have an exchange privilege with certain other Funds. However, Investor A1, Investor B1, Investor C1, Investor C2 and Investor C3 Shares may only exchange out. The minimum amount for exchanges of Investor class shares is $1,000, although you may exchange less than $1,000 if you already have an account in the Fund into which you are exchanging. You may only exchange into a share class and a Fund that are open to new investors or in which you have a current account if the class or fund is closed to new investors. Before effecting an exchange, you should obtain a currently effective prospectus of the fund into which you wish to make the exchange. Exercise of the exchange privilege is treated as a sale of the exchanged shares and a purchase of the acquired shares for Federal income tax purposes.

The section entitled “Shareholder Services—Exchange Privilege—Exchanges of Investor A, Investor A1, Institutional and Institutional Daily Shares” in Part II of each Fund’s SAI is deleted in its entirety and replaced with the following:

Exchanges of Investor A, Investor A1, Class K and Institutional Shares. Institutional Shares are exchangeable with Institutional Shares of other Funds. Investor A and Investor A1 Shares are exchangeable for Investor A Shares of other Funds. Class K Shares are exchangeable for Class K Shares of other Funds.

Exchanges of Institutional Shares outstanding for Institutional Shares of a second fund or for shares of a money market fund are effected on the basis of relative net asset value per Institutional Share. Exchanges of Investor A or Investor A1 Shares outstanding (“outstanding Investor A Shares”) for Investor A Shares of a second fund, or for shares of a money market fund (“new Investor A Shares”) are effected on the basis of relative net asset value per share. Exchanges of Class K Shares outstanding for Class K Shares of a second fund, or for shares of a money market fund are effected on the basis of relative net asset value per share.

Shareholders should retain this Supplement for future reference.

SAI-MULTIEX-K0517SUP

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