At a glance
MBB charges 0.04% a year, below the 0.32% average of the 7 funds most like it (the 2nd cheapest of 8). It has $39.63B in assets, the largest of that group; it paid 4.43% of its price in distributions over the past 12 months, monthly. Over the past year it returned +0.2% with distributions reinvested, 4th of those 8 funds; over three years it returned +5.6% a year. At its worst it fell 4.3% in the 2020 crash (S&P 500: 33.7%) and 14.4% in the 2022 bear market (S&P 500: 24.5%), and was back at its earlier high within a month and 35 months after the lows. Its ten largest positions make up 6.6% of the fund, out of 11,209 in all.
The short version
iShares MBS ETF (MBB) is a BlackRock index fund that tracks the Bloomberg U.S. MBS Index: fixed-rate mortgage-backed bonds issued or guaranteed by Ginnie Mae, Fannie Mae and Freddie Mac. It costs 0.04% a year, far less than the 0.32% average for similar funds, though Vanguard's closely matched VMBS charges 0.03%. It pays income monthly. With $39.6 billion in assets as of August 31, 2026, it is the largest fund among its peers.
Price history
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MBB +0.2% over the year to Nov 2, 2026, total return with distributions reinvested.
How it has behaved
| YTD | 1 yr | 3 yr | 5 yr | 10 yr | Since start | |
|---|---|---|---|---|---|---|
| MBB official prospectus, to Dec 31, 2025 | — | +8.45% | — | +0.08% | +1.49% | — |
| Bloomberg US Universal Index index, same period | — | +7.58% | — | +0.06% | +2.44% | — |
| MBB price data to Nov 2, 2026 | -0.5% | +0.2% | +5.6% | +0.2% | +1.1% | +2.6% |
- Over the year to Nov 2, 2026, MBB returned +0.2%, 4th of 8 among similar funds.
- Its 5-year annualized return was +0.2% and its 10-year +1.1%.
- In the 2020 COVID crash, while stocks fell, it gained 0.1%.
- Its worst full calendar year was 2022 (-11.7%); its best was 2025 (+8.4%).
- The deepest fall in its price history was 17.6% (Feb 9, 2021 to Oct 19, 2023), recovered by Oct 28, 2025.
Show as a table
| Year | Price data | Prospectus (official) |
|---|---|---|
| 2026 (to date) | -0.5% | — |
| 2025 | +8.4% | +8.45% |
| 2024 | +1.3% | +1.31% |
| 2023 | +5.0% | +4.99% |
| 2022 | -11.7% | -11.86% |
| 2021 | -1.4% | -1.27% |
| 2020 | +4.1% | +4.03% |
| 2019 | +6.2% | +6.27% |
| 2018 | +0.8% | +0.81% |
| 2017 | +2.5% | +2.37% |
| 2016 | +1.3% | +1.28% |
| 2015 | +1.1% | — |
| 2014 | +6.4% | — |
| 2013 | -1.9% | — |
| 2012 | +2.0% | — |
| 2011 | +5.9% | — |
| 2010 | +5.6% | — |
| 2009 | +4.7% | — |
| 2008 | +7.7% | — |
| 2008 financial crisis stocks fell Oct 9, 2007 – Mar 9, 2009 | Gained 11.5% over that stretch · deepest drop along the way 3.8%, back to its old high 0.9 months after the low |
|---|---|
| 2020 COVID crash stocks fell Feb 19, 2020 – Mar 23, 2020 | Gained 0.1% over that stretch · deepest drop along the way 4.3%, back to its old high 0.5 months after the low |
| 2022 bear market stocks fell Jan 3, 2022 – Oct 12, 2022 | Lost 13.8% over that stretch · deepest drop along the way 14.4%, back to its old high 35.3 months after the low |
Dividends and income
Show as a table
| Year | Per share | Change |
|---|---|---|
| 2026 (to date) | $3.0434 | |
| 2025 | $4.0100 | +11.1% |
| 2024 | $3.6100 | +13.2% |
| 2023 | $3.1900 | +47.7% |
| 2022 | $2.1600 | +89.5% |
| 2021 | $1.1400 | -50.9% |
| 2020 | $2.3200 | -22.4% |
| 2019 | $2.9900 | +9.1% |
| 2018 | $2.7400 | +15.6% |
| 2017 | $2.3700 | -13.8% |
| 2016 | $2.7500 | -4.2% |
| 2015 | $2.8700 | +52.7% |
| 2014 | $1.8800 | +39.3% |
| 2013 | $1.3500 | -38.6% |
| 2012 | $2.2000 | -38.7% |
| 2011 | $3.5900 | -42.5% |
| 2010 | $6.2400 | +65.1% |
| 2009 | $3.7800 | -16.6% |
| 2008 | $4.5300 |
What's inside
As of Aug 31, 2026, the fund held 11,209 securities; the ten largest made up 6.6% of assets, and 7.6% sat in cash and money-market holdings.
| Holding | Weight | |
|---|---|---|
| Government National Mortgage Association Mortgage-backed securities | 1.05% | |
| Freddie Mac Mortgage-backed securities | 0.98% | |
| UMBS, TBA Mortgage-backed securities | 0.85% | |
| UMBS, TBA Mortgage-backed securities | 0.70% | |
| Government National Mortgage Association Mortgage-backed securities | 0.53% | |
| Government National Mortgage Association Mortgage-backed securities | 0.51% | |
| Government National Mortgage Association Mortgage-backed securities | 0.51% | |
| Government National Mortgage Association Mortgage-backed securities | 0.50% | |
| Government National Mortgage Association Mortgage-backed securities | 0.49% | |
| Fannie Mae Mortgage-backed securities | 0.49% | |
| Government National Mortgage Association Mortgage-backed securities | 0.48% | |
| Freddie Mac Mortgage-backed securities | 0.47% | |
| Government National Mortgage Association Mortgage-backed securities | 0.46% | |
| Fannie Mae Mortgage-backed securities | 0.41% | |
| Fannie Mae Mortgage-backed securities | 0.41% |
By country
United States 98.22%By issuer
US government-sponsored enterprises 74.84%US government agencies 23.38%The bonds mature in 24.2 years on average (weighted by size), with an average coupon of 3.72%.
Source: N-PORT holdings report as of Aug 31, 2026. Cash, money-market funds and derivatives are shown separately from the securities list.What changed recently
- Over the three months to Aug 31, 2026, investors added a net $1.60B (creations minus redemptions, per the N-PORT report).
- Monthly total returns reported for that quarter: +0.21%, -1.42%, +0.51%.
How it works
MBB tracks the Bloomberg U.S. MBS Index. Mortgage-backed securities (MBS) are bonds built from pools of home loans. Homeowners' monthly payments, including early payoffs, pass through to the bondholders. The index holds investment-grade, fixed-rate pools with 15-, 20- and 30-year terms, issued or guaranteed by Ginnie Mae, Fannie Mae and Freddie Mac. Bloomberg weights the pools by market value and updates the index on the last business day of each month. The index had 1,047 issues as of February 28, 2026.
The fund regularly buys through to-be-announced (TBA) contracts. A TBA contract fixes a price now but names the exact mortgage pools only a few days before settlement. Until then, the fund holds short-term instruments, including BlackRock money market funds, and pays its share of their fees. Cash made up 7.6% of the fund as of August 31, 2026. The prospectus filed June 18, 2026, lists turnover of 153%. The fund itself treats anything above 100% as high, and that much trading adds costs.
BlackRock uses representative sampling. Instead of buying every pool, it holds a mix that matches the index's yield, credit quality, maturity and duration (how much prices move when interest rates change). At least 80% of assets must be in index securities or TBAs with nearly identical features. Up to 10% may go to futures, options, swaps or other bonds. As of August 31, 2026, the fund held no derivatives. About 75% of assets was in Fannie Mae and Freddie Mac securities and 23% in Ginnie Mae.
What it really costs
- MBB charges 0.04% a year, versus an average of 0.32% for the similar funds below (2nd of 8, cheapest first).
- Using the prospectus's standard example, $10,000 invested would cost about $4 in the first year and $51 over 10 years (assuming a 5% annual return).
| Cost of $10,000 (SEC example) | 1 yr | 3 yrs | 5 yrs | 10 yrs |
|---|---|---|---|---|
| MBB | $4 | $13 | $23 | $51 |
Structure and tax notes
- Bond prices move opposite to interest rates; the longer the maturities it holds, the more its price reacts to rate changes.
In a retirement portfolio
Its mortgage bonds, guaranteed by Ginnie Mae, Fannie Mae and Freddie Mac, rose during the 2008 stock crash and were roughly flat in 2020, though they fell sharply in 2022.
MBB held up when stocks crashed in 2008 and 2020. From the market's October 2007 peak to its March 2009 low, the fund gained 11.5%, and it was roughly flat through the 2020 COVID crash. The 2022 market slump hit it hard, though. It lost 11.86% that year, its worst calendar year. Its deepest drop, 17.6% from February 2021 to October 2023, took until October 2025 to recover. Anyone drawing cash from it in those years would have been withdrawing at lower prices.
Over the 12 months to October 27, 2026, it paid out 4.44% of its price in income, in monthly payments. Those payouts can shrink when falling rates lead homeowners to refinance. Costs are low: the SEC's standard $10,000 example comes to $4 after one year and $51 over 10 years. Past results don't predict the future, and a plan should look at the whole portfolio, not one fund.
Who it may suit — and who should look elsewhere
May suit
- Investors wanting cheap exposure to Ginnie Mae, Fannie Mae and Freddie Mac mortgage bonds: the 0.04% fee is far below the 0.32% peer average.
- Retirees who value monthly income: payouts over the 12 months to October 27, 2026, equaled a 4.44% yield.
- Investors seeking a counterweight to stocks: the fund gained 11.5% from the market's October 2007 peak to its March 2009 low.
Look elsewhere if
- Investors uneasy with long recoveries: after a 17.6% slide that began in February 2021, the fund didn't regain its high until October 2025.
- Anyone seeking a one-stop bond fund: about 98% of assets were in mortgage-backed securities as of August 31, 2026.
- Those wanting predictable cash flows: falling rates bring early loan payoffs that can cut income, and rising rates slow repayments and can push prices down.
Close alternatives
Matched by bond funds with the closest average maturity and issuer mix (N-PORT).
| Fund | Avg. maturity | Cost | Net assets | 1 yr | 3 yr |
|---|---|---|---|---|---|
| MBB this fund | 24.2 yrs | 0.04% | $39.63B | +0.2% | +5.6% |
| VMBS Vanguard Mortgage-Backed Securities ETF | 23.9 yrs | 0.03% | $17.59B | +1.0% | +6.6% |
| SPMB SPDR Portfolio Mortgage Backed Bond ETF | 24.9 yrs | 0.04% | $7.07B | -0.7% | +6.0% |
| FSEC Fidelity Investment Grade Securitized ETF | 23.6 yrs | 0.36% | $4.64B | -0.7% | +6.4% |
| JMBS Janus Henderson Mortgage-Backed Securities … | 28 yrs | 0.22% | $6.68B | -1.0% | +6.2% |
| LGOV First Trust Long Duration Opportunities ETF | 20.4 yrs | 0.66% | $619.4M | -4.0% | +5.5% |
| LMBS First Trust Low Duration Opportunities ETF | 19.4 yrs | 0.65% | $6.35B | +2.0% | +6.0% |
| CMBS iShares CMBS ETF | 16.2 yrs | 0.25% | $472.9M | +0.4% | +5.9% |
Questions investors ask
Does MBB pay monthly dividends?
Yes. MBB pays income every month. Over the 12 months to October 27, 2026, it paid about $4.06 per share. That is a trailing yield of 4.44% (past-year income divided by the share price). The payouts come from interest on the mortgage bonds it owns, so they aren't fixed. If falling rates lead homeowners to refinance, the fund may have to reinvest at lower yields, and income can shrink.
What's the difference between MBB and VMBS?
Very little. Vanguard Mortgage-Backed Securities ETF (VMBS) is the closest match in our comparison, 98% similar on average maturity and issuer mix. VMBS charges 0.03% a year versus MBB's 0.04%. Through October 27, 2026, VMBS lost 0.2% over one year and returned 6.2% a year over three years. MBB lost 0.6% and returned 6.1% over the same periods. MBB is larger: $39.6 billion in net assets as of August 31, 2026, versus $17.0 billion for VMBS as of May 31, 2026.
Is MBB safe?
It carries limited credit risk, but it can still lose money. Its bonds are issued or guaranteed by Ginnie Mae, Fannie Mae and Freddie Mac. Even so, the prospectus notes that some MBS are not backed by the full faith and credit of the U.S. government. Prices also move with interest rates. MBB lost 11.86% in 2022, and its deepest drop, 17.6% from February 2021 to October 2023, took until October 2025 to recover.
How do interest rates affect MBB?
Rising rates usually push MBB's price down, because bond prices move opposite to rates. Mortgage bonds add a twist. When rates climb, fewer homeowners refinance and they pay off loans more slowly, so values can fall sharply (extension risk). When rates fall, homeowners refinance and repay early. The fund may then have to reinvest at lower yields, which can shrink income (prepayment risk). As of August 31, 2026, holdings averaged 24.2 years to maturity and a 3.72% coupon, or interest rate.
What has MBB returned over 10 years?
About 1.5% a year. The prospectus shows average annual returns of 1.49% over the 10 years to December 31, 2025, and 0.08% over five years, despite an 8.45% gain in 2025. The broad Bloomberg US Universal Index, which the prospectus uses for comparison, returned 2.44% a year over the same 10 years. Through October 27, 2026, MBB's 10-year return was 1.1% a year. Its worst calendar year from 2016 to 2025 was 2022, when it lost 11.86%.