BlackRock Asian Dragon Fund, Inc.

BLACKROCK FUNDSSM iShares Total U.S. Stock Market Index Fund

(the "Fund")

Supplement dated March 10, 2021 to the Summary Prospectuses and the Prospectuses of the Fund, each dated November 27, 2020, as supplemented to date

Effective immediately, the following changes are made to the Fund's Summary Prospectuses and Prospectuses, as applicable:

The section of the Summary Prospectuses entitled "Key Facts About iShares Total U.S. Stock Market Index Fund -- Portfolio Managers" and the section of the Prospectuses entitled "Fund Overview -- Key Facts About iShares Total U.S. Stock Market Index Fund -- Portfolio Managers" are deleted in their entirety and replaced with the following:

Name Alan Mason Suzanne Henige, CFA Jennifer Hsui, CFA Amy Whitelaw

Portfolio Manager of the Fund Since 2015 2020 2016 2019

Title Managing Director of BlackRock, Inc.

Director of BlackRock, Inc. Managing Director of BlackRock, Inc. Managing Director of BlackRock, Inc.

The section of the Prospectuses entitled "Details About the Fund -- How the Fund Invests -- About the Portfolio Management Team of the Fund" is deleted in its entirety and replaced with the following:

ABOUT THE PORTFOLIO MANAGEMENT TEAM OF THE FUND The Fund is managed by a team of financial professionals. Alan Mason, Suzanne Henige, CFA, Jennifer Hsui, CFA, and Amy Whitelaw are the portfolio managers and are jointly and primarily responsible for the day-to-day management of the Fund. See "Management of the Fund -- Portfolio Manager Information" for additional information about the portfolio management team.

The section of the Prospectuses entitled "Management of the Fund -- Portfolio Manager Information" is deleted in its entirety and replaced with the following:

Information regarding the portfolio managers of the Fund is set forth below. Further information regarding the portfolio managers, including other accounts managed, compensation, ownership of Fund shares, and possible conflicts of interest, is available in the Fund's SAI.

Portfolio Manager Primary Role

Alan Mason

Jointly and primarily responsible for the day-to-day management of the Fund's portfolio, including setting the Fund's overall investment strategy and overseeing the management of the Fund.

Suzanne Henige, CFA

Jointly and primarily responsible for the day-to-day management of the Fund's portfolio, including setting the Fund's overall investment strategy and overseeing the management of the Fund.

Since Title and Recent Biography

2015

Managing Director of BlackRock, Inc. since 2009; Managing Director of Barclays Global Investors ("BGI") from 2008 to 2009; Principal of BGI from 1996 to 2008.

2020 Director of BlackRock, Inc. since 2016; Vice President of BlackRock, Inc. from 2011 to 2015.

Portfolio Manager Primary Role

Jennifer Hsui, CFA

Jointly and primarily responsible for the day-to-day management of the Fund's portfolio, including setting the Fund's overall investment strategy and overseeing the management of the Fund.

Amy Whitelaw

Jointly and primarily responsible for the day-to-day management of the Fund's portfolio, including setting the Fund's overall investment strategy and overseeing the management of the Fund.

Since Title and Recent Biography

2016

Managing Director of BlackRock, Inc. since 2011; Director of BlackRock, Inc. from 2009 to 2011; Principal of BGI from 2006 to 2009.

2019

Managing Director of BlackRock, Inc. since 2013; Director of BlackRock, Inc. from 2009 to 2012; Principal of BGI from 2000 to 2009.

Shareholders should retain this Supplement for future reference.

ALLPRO-TSMI-0321SUP

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Table of Contents

Prospectus

BlackRock FundsSM | Class K Shares ? iShares Total U.S. Stock Market Index Fund

Class K: BKTSX

NOVEMBER 27, 2020

Beginning on January 1, 2021, as permitted by regulations adopted by the Securities and Exchange Commission, paper copies of the Fund's shareholder reports will no longer be sent by mail, unless you specifically request paper copies of the reports from BlackRock or from your financial intermediary, such as a broker-dealer or bank. Instead, the reports will be made available on a website, and you will be notified by mail each time a report is posted and provided with a website link to access the report.

You may elect to receive all future reports in paper free of charge. If you hold accounts directly with BlackRock, you can call (800) 537-4942 to inform BlackRock that you wish to continue receiving paper copies of your shareholder reports. If you hold accounts through a financial intermediary, you can follow the instructions included with this disclosure, if applicable, or contact your financial intermediary to request that you continue to receive paper copies of your shareholder reports. Please note that not all financial intermediaries may offer this service. Your election to receive reports in paper will apply to all funds advised by BlackRock Advisors, LLC, BlackRock Fund Advisors or their affiliates, or all funds held with your financial intermediary, as applicable.

If you already elected to receive shareholder reports electronically, you will not be affected by this change and you need not take any action. You may elect to receive electronic delivery of shareholder reports and other communications by: (i) accessing the BlackRock website at edelivery and logging into your accounts, if you hold accounts directly with BlackRock, or (ii) contacting your financial intermediary, if you hold accounts through a financial intermediary. Please note that not all financial intermediaries may offer this service.

This Prospectus contains information you should know before investing, including information about risks. Please read it before you invest and keep it for future reference.

The Securities and Exchange Commission has not approved or disapproved these securities or passed upon the adequacy of this Prospectus. Any representation to the contrary is a criminal offense.

Not FDIC Insured ? May Lose Value ? No Bank Guarantee

Table of Contents

Table of Contents

Fund Overview

Key facts and details about the Fund, including investment objective, principal investment strategies, principal risk factors, fee and expense information and historical performance information Investment Objective ................................................................................ 3 Fees and Expenses of the Fund ................................................................. 3 Principal Investment Strategies of the Fund ................................................ 4 Principal Risks of Investing in the Fund ...................................................... 4 Performance Information .......................................................................... 5 Investment Manager ................................................................................. 6 Portfolio Managers ................................................................................... 6 Purchase and Sale of Fund Shares ............................................................ 6 Tax Information......................................................................................... 7 Payments to Broker/Dealers and Other Financial Intermediaries .................. 7

Details About the Fund

Information about how the Fund invests, including investment objective, investment process, principal strategies and risk factors How the Fund Invests................................................................................ 8 Investment Risks...................................................................................... 9

Account Information

Information about account services, sales charges and waivers, shareholder transactions, and distribution and other payments Details About the Share Class ................................................................. 16 How to Buy, Sell, Exchange and Transfer Shares ....................................... 17 Fund's Rights ......................................................................................... 22 Short-Term Trading Policy ........................................................................ 22

Management of the Fund

Information about BlackRock and the Portfolio Managers BlackRock.............................................................................................. 24 Portfolio Manager Information ................................................................. 25 Conflicts of Interest ................................................................................ 26 Valuation of Fund Investments ................................................................. 27 Dividends, Distributions and Taxes........................................................... 28

Financial Highlights Financial Performance of the Fund........................................................... 30

General Information Shareholder Documents.......................................................................... 31

Certain Fund Policies .............................................................................. 31 Statement of Additional Information ......................................................... 32

Glossary Glossary of Investment Terms ................................................................. 33

For More Information Fund and Service Providers ............................................... Inside Back Cover

Additional Information.......................................................

Back Cover

Table of Contents

Fund Overview

Key Facts About iShares Total U.S. Stock Market Index Fund

Investment Objective

The investment objective of iShares Total U.S. Stock Market Index Fund (the "Fund"), a series of BlackRock FundsSM (the "Trust"), is to seek to track the investment results of a broad-based index composed of U.S. equities.

Fees and Expenses of the Fund

This table describes the fees and expenses that you may pay if you buy and hold Class K Shares of the Fund.

Annual Fund Operating Expenses (expenses that you pay each year as a percentage of the value of your investment)

Class K Shares

Management Fee1

0.01%

Distribution and/or Service (12b-1) Fees

None

Other Expenses

0.03%

Total Annual Fund Operating Expenses

0.04%

Fee Waivers and/or Expense Reimbursements1,2

(0.01)%

Total Annual Fund Operating Expenses After Fee Waivers and/or Expense Reimbursements1,2

0.03%

1 As described in the "Management of the Fund" section of the Fund's prospectus beginning on page 24, BlackRock Advisors, LLC ("BlackRock") has contractually agreed to waive the management fee with respect to any portion of the Fund's assets estimated to be attributable to investments in other equity and fixed-income mutual funds and exchange-traded funds managed by BlackRock or its affiliates that have a contractual management fee, through November 30, 2021. In addition, 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 November 30, 2021. The contractual agreements may be terminated upon 90 days' notice by a majority of the noninterested trustees of the Trust or by a vote of a majority of the outstanding voting securities of the Fund.

2 As described in the "Management of the Fund" section of the Fund's prospectus beginning on page 24, 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 0.03% of average daily net assets through November 30, 2021. The Fund may have to repay some of these waivers and/or reimbursements to BlackRock in the following two years, and such repayment arrangement will terminate on August 13, 2022. 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.

Example: This Example is intended to help you compare the cost of investing in shares of the Fund with the cost of investing in other mutual funds. The Example assumes that you invest $10,000 in shares of the Fund for the time periods indicated and then redeem all of your shares at the end of those periods. The Example also assumes that your investment has a 5% return each year and that the Fund's operating expenses remain the same. Although your actual costs may be higher or lower, based on these assumptions your costs would be:

Class K Shares

1 Year $3

3 Years $12

5 Years $22

10 Years $50

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 15% of the average value of its portfolio.

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