iShares MBS ETF
iShares · Tracks Bloomberg US MBS Index · Inception Mar 13, 2007
Trailing returns
through Oct 23, 2026- 1 year
- -0.1%
- 3 year
- +6.1%
- annualized
- 5 year
- +0.1%
- annualized
Price return from month-end closes, distributions reinvested at month end. Excludes trading costs, bid-ask spreads and taxes. Past performance says nothing about future returns and is not part of the composite score — see the methodology for what the score does measure.
Composite score
Based on a 0.040% expense ratio.
Based on $36.25B in net assets.
Top-10 holdings represent 6.8% of net assets.
US Aggregate Bond base · ETF wrapper · 4.46% TTM yield.
The composite is a weighted average of the four core sub-scores above (cost, tax efficiency, liquidity, concentration). Missing sub-scores fall back to the per-category median when the category has at least 50% data coverage, so funds without (e.g.) parsed N-PORT holdings aren't accidentally boosted by renormalization. Tracking quality is shown where computable but isn't currently part of the composite weighting. See methodology for formulas, the tracking-quality partial-coverage rationale, and the dimensions we deliberately don't score (methodology v0.5.2).
Look through MBB, or compare the fee
Tool · Look-through
Underlying holdings, with other funds added
Add tickers and weights; N-PORT positions are summed across the basket.
Tool · Cost
Compare MBB's fee against another fund
Compounds the 0.040% expense ratio against a peer over decades.
Tool · Overlap
Compare MBB's holdings with peers
Pairwise holdings heatmap, pre-loaded with similar US Aggregate Bond funds.
Tool · TLH
Find a tax-loss harvesting partner for MBB
Ranks every catalog fund by holdings overlap, flags wash-sale risk.
Tool · Placement
Asset location for MBB across account types
Asset-location optimizer — places each fund in taxable / tax-deferred / Roth.
Top holdings
| # | Holding | Weight |
|---|---|---|
| 1 | Freddie Mac | 1.05% |
| 2 | Government National Mortgage Association | 0.95% |
| 3 | UMBS, TBA | 0.83% |
| 4 | Government National Mortgage Association | 0.67% |
| 5 | UMBS, TBA | 0.64% |
| 6 | Government National Mortgage Association | 0.55% |
| 7 | Government National Mortgage Association | 0.54% |
| 8 | Government National Mortgage Association | 0.53% |
| 9 | Fannie Mae | 0.52% |
| 10 | Freddie Mac | 0.50% |
Compare MBB with another fund
Or skim the closest-overlap funds below.
Similar ETFs by holdings overlap
- VMBS Vanguard Mortgage-Backed Securities Index Fund ETF Shares 17.2% overlap
- AGG iShares Core U.S. Aggregate Bond ETF 16.7% overlap
- SPMB State Street SPDR Portfolio Mortgage Backed Bond ETF 14.5% overlap
- EAGG iShares ESG U.S. Aggregate Bond ETF 12.9% overlap
- IUSB iShares Core Universal USD Bond ETF 9.0% overlap
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