ETF comparison
MBB vs SPMB
Both US Aggregate Bond.
iShares MBS ETF · State Street SPDR Portfolio Mortgage Backed Bond Index ETF
Holdings overlap
840 positions appear in both funds. Buying equal dollars of MBB and SPMB would leave roughly 14.9% of each dollar exposed to the same underlying securities.
Unmatched is the part of a fund's weight the other fund doesn't match: names only it holds, plus any extra weight it puts in names both funds hold.
Side by side
Sub-score comparison
Tracking quality isn't part of the composite — see what we don't score for why.
Cost difference
Expense ratios are effectively identical (0.040% vs 0.040%).
Fee figure is the annual expense charged on $100,000. To see how the gap compounds over a multi-decade holding period, open the cost calculator pre-filled with MBB vs SPMB.
Top shared holdings
840 shared in total| # | Holding | In MBB | In SPMB | Overlap |
|---|---|---|---|---|
| 1 | Fannie Mae | 0.41% | 0.47% | 0.41% |
| 2 | Government National Mortgage Association | 0.40% | 0.32% | 0.32% |
| 3 | Government National Mortgage Association | 0.30% | 0.30% | 0.30% |
| 4 | Freddie Mac | 0.47% | 0.30% | 0.30% |
| 5 | Fannie Mae | 0.29% | 0.37% | 0.29% |
| 6 | Fannie Mae | 0.28% | 0.26% | 0.26% |
| 7 | Government National Mortgage Association | 0.28% | 0.25% | 0.25% |
| 8 | Government National Mortgage Association | 0.26% | 0.25% | 0.25% |
| 9 | Freddie Mac | 0.23% | 0.29% | 0.23% |
| 10 | Government National Mortgage Association | 0.33% | 0.22% | 0.22% |
| 11 | Government National Mortgage Association | 0.50% | 0.20% | 0.20% |
| 12 | Fannie Mae | 0.20% | 0.45% | 0.20% |
Only in MBB
10,369 total- Government National Mortgage Association 1.05%
- Freddie Mac 0.98%
- UMBS, TBA 0.85%
- UMBS, TBA 0.70%
- Government National Mortgage Association 0.53%
- Government National Mortgage Association 0.51%
- Government National Mortgage Association 0.51%
- Government National Mortgage Association 0.49%
- Fannie Mae 0.49%
- Government National Mortgage Association 0.46%
Only in SPMB
1,859 total- Freddie Mac 1.17%
- Freddie Mac 0.76%
- UMBS, TBA 0.63%
- Freddie Mac 0.61%
- Freddie Mac 0.55%
- Fannie Mae 0.51%
- UMBS, TBA 0.46%
- UMBS, TBA 0.45%
- Government National Mortgage Association 0.44%
- Freddie Mac 0.44%
Related comparisons
More comparisons with MBB
- MBB vs EAGG · iShares ESG U.S. Aggregate Bond ETF 12.7%
- MBB vs IUSB · iShares Core Universal USD Bond ETF 9.5%
- MBB vs SCHZ · Schwab U.S. Aggregate Bond ETF 6.9%
- MBB vs SPAB · State Street SPDR Portfolio Aggregate Bond Index ETF 5.8%
- MBB vs BND · Vanguard Total Bond Market Index Fund ETF Shares 5.4%
- MBB vs FBND · Fidelity Total Bond ETF 5.2%
More comparisons with SPMB
- SPMB vs SCHZ · Schwab U.S. Aggregate Bond ETF 8.9%
- SPMB vs BND · Vanguard Total Bond Market Index Fund ETF Shares 5.9%
- SPMB vs AGG · iShares Core U.S. Aggregate Bond ETF 5.4%
- SPMB vs VCRB · Vanguard Core Bond ETF 4.9%
- SPMB vs CGCP · Capital Group Core Plus Income ETF 3.8%
- SPMB vs EAGG · iShares ESG U.S. Aggregate Bond ETF 3.8%
Percentages are holdings overlap with the named fund.
Open MBB or SPMB at a brokerage
Both funds trade commission-free at major US brokerages.
Affiliate links — opening an account through these earns PlainIndex a one-time referral. Scoring is computed before any affiliate consideration; see our methodology and funding disclosure.
Holdings overlap is the sum of min(weight_a, weight_b) over positions
matched on ISIN (CUSIP fallback). Methodology: see
/methodology/.
Comparing two funds doesn't endorse swapping one for the other. Tax-lot history, account type, and personal goals matter — PlainIndex publishes data and methodology, not investment advice.