iShares MBS ETF
U.S. bond index ETF · tracks Bloomberg U.S. MBS Index
As of its 2026 Q2 report, iShares MBS ETF held 11,145 positions with $38.74B in net assets. Its ten largest holdings made up 13.1% of the fund. The MBB share class costs 0.04% a year. Over the 12 months to May 2026, MBB returned 6.8%, with dividends reinvested. In 2026 Q2 it added 100 new positions and exited 107.
The iShares MBS ETF (the Fund ) seeks to track the investment results of an index composed of investment-grade, mortgage-backed pass-through securities issued and/or guaranteed by U.S. government agencies.
The fund tracks the Bloomberg U.S. MBS Index using representative sampling, holding a sample of investment-grade mortgage-backed securities issued or guaranteed by Ginnie Mae, Fannie Mae, and Freddie Mac with 15-, 20-, or 30-year maturities. The fund invests at least 80% of assets in index components or to-be-announced MBS contracts with substantially identical economic characteristics, and may use up to 10% in derivatives or non-index fixed income securities to track the index. Because the fund does not hold all index constituents, its returns may diverge from the index.
What you own
| Company | Weight | Value | Shares |
|---|---|---|---|
BLACKROCK CASH FUNDS TREASURY SL AGENCY SHARES | 6.77% | $2.62B | — |
Freddie Mac 2.00% · due 2051-05-01 | 1.05% | $405.59M | — |
Government National Mortgage Association 5.50% · due 2056-06-20 | 0.95% | $367.08M | — |
UMBS, TBA 5.50% · due 2056-06-01 | 0.83% | $322.19M | — |
Government National Mortgage Association 5.00% · due 2056-06-20 | 0.67% | $260.19M | — |
UMBS, TBA 5.00% · due 2056-06-01 | 0.64% | $249.20M | — |
Government National Mortgage Association 5.00% · due 2054-11-20 | 0.55% | $212.99M | — |
Government National Mortgage Association 2.00% · due 2051-10-20 | 0.54% | $209.88M | — |
Government National Mortgage Association 2.00% · due 2051-12-20 | 0.53% | $206.31M | — |
Fannie Mae 2.00% · due 2051-12-01 | 0.52% | $202.25M | — |
The 200 largest of 11,145 holdings, with the share counts as filed, open with a free account.
What the fund is made of
Percentages are of fund net assets. Rounding, liabilities and short positions can make totals differ from 100%.
| Securitized | 98.10% |
| Cash & short-term | 6.77% |
How it has done
MBB share class · total returns with dividends reinvested
Volatility over the last 12 months: 3.36%. Past returns are a record, not a forecast.
Fees & fund details
iShares MBS ETF is a U.S. bond index ETF that tracks the Bloomberg U.S. MBS Index.
- Asset class
- Bonds
- Region
- United States
- Management
- Index (passive)
- Fund type
- ETF
- Credit quality
- Investment grade
- Rate sensitivity
- Intermediate duration
- Expense ratio, by class
- 0.04%· MBB 0.04%
- Portfolio turnover
- 153.00% a year · as of 2026 Q2
Turnover is how much of the portfolio was replaced in a year.
Classified from what the fund holds, not from its name · 2026 Q2. The summary is a paraphrase of the prospectus; the objective is verbatim.
What changed this quarter
Positions that entered or left the fund since its previous filing. Positions that were only resized are not listed.
100 new· the largest 2
107 exited· the largest 2
Debt profile
What this fund holds — value-weighted across its bond and securitized long positions · as of 2026-05-31
Share of the fund's debt by how its coupon behaves — the fact that decides whether a rate move reaches this portfolio at all.
| Fixed rate | 100.0% |
| Floating rate | 0.0% |
Share of the fund's debt value in each maturity band, shortest first.
| <1y | 0.0% |
| 1-3y | 0.0% |
| 3-5y | 0.2% |
| 5-10y | 3.1% |
| 10y+ | 96.7% |
Based on what filers reported; a filer that never reported a flag also reads as none.
Risk profile
Interest-rate and credit-spread sensitivity, both in years · as of 2026Q2
Most of this fund’s sensitivity is to interest rates, with credit spreads carrying nearly as much.
Where the loss would come from. The two shocks are the same size, so this is the balance of the fund's two sensitivities rather than a bet on one moving more.
| Interest rates | 51% |
| Credit spreads | 49% |
Filers report the impact of a 0.01% move only, so the total is our own scaling of that one number and overstates the loss on most bonds — read it as approximate, never as precise. The two sensitivities overlap rather than add up: they measure the same positions against different shocks, which is why the durations above are shown side by side and never summed.
Share of the fund's spread duration carried by each credit tier.
| Investment grade | +5.28 yr |
| High yield | +0.01 yr |
Share of duration at each point, shortest first. A positive figure loses value when spreads widen; a negative one offsets — a credit hedge.
| 1 yr | 0.38 yr | 7% |
| 5 yr | 1.89 yr | 35% |
| 10 yr | 2.19 yr | 40% |
| 30 yr | 0.96 yr | 18% |
3 mo is NEGATIVE (-0.00 yr) — a deliberate hedge at that point on the curve, so it is not part of the band above.
| 3 mo | 0.01 yr | 0% |
| 1 yr | 0.02 yr | 0% |
| 5 yr | 4.04 yr | 76% |
| 10 yr | 1.22 yr | 23% |
The two bands measure the same positions against different shocks and do not add — a Treasury carries rate duration and no spread duration, a floating-rate credit the reverse. Rate tenors are also summed across every currency the fund discloses.
Show the numbers
| Tenor | Rate yrs | IG yrs | HY yrs | IG $/bp | HY $/bp |
|---|---|---|---|---|---|
| 3 mo | -0.00 | +0.00 | +0.01 | $917 | $56.9k |
| 1 yr | +0.38 | +0.02 | +0.00 | $85.4k | $0 |
| 5 yr | +1.89 | +4.04 | +0.00 | $15.65m | $0 |
| 10 yr | +2.19 | +1.22 | +0.00 | $4.72m | $0 |
| 30 yr | +0.96 | +0.00 | +0.00 | $0 | $0 |
Dollar change per 1bp of spread movement, as filed and sign-anchored. A blank cell was not filed; a zero was.
Understand how this fund fits with the rest.
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