VMBS vs MBB: Holdings Overlap
VMBSVanguard Mortgage-backed Securities Index Fund
Vanguard · 5112 holdings · $15.6B · as of 2026-05-31
iShares · 11144 holdings · $39.1B · as of 2026-05-31
How similar are VMBS and MBB?
Vanguard Mortgage-backed Securities Index Fund (VMBS, by Vanguard) holds 5112 positions; iShares MBS ETF (MBB, by iShares) holds 11144. They have 1212 holdings in common, and by portfolio weight the two funds are 17.2% identical. In practical terms the pair is lightly overlapping, with most of each portfolio distinct.
- Overlap by Weight
- 17.2%Sum of the smaller weight of each shared holding
- Shared Holdings
- 1212VMBS holds 5112 · MBB holds 11144
- Weight in Shared Holdings
- VMBS 34%·MBB 32%Share of each fund's weight in stocks both funds own
Based on each fund's latest official holdings. How is this calculated?
What makes each fund different
Only in VMBS
3900 of 5112 positions (65.8% of the fund) are not held by MBB. Showing the top 30 by weight.
- G2SF 5.5 7/260.36%
- FN CC27620.29%
- FR SD41550.27%
- FR RQ01180.27%
- Uniform Mortgage-Backed Security, TBA0.25%
- FR RQ00940.24%
Only in MBB
9932 of 11144 positions (66.2% of the fund) are not held by VMBS. Showing the top 30 by weight.
- Ginnie Mae II Pool0.53%
- Fannie Mae Pool0.52%
- Ginnie Mae0.46%
- Fannie Mae Pool0.44%
- Fannie Mae Pool0.44%
- Fannie Mae Pool0.33%
Performance
| Fund | 1M | YTD | 1Y | 3Y (ann.) | 5Y (ann.) | 10Y (ann.) | Yield |
|---|---|---|---|---|---|---|---|
| VMBS | -0.1% | +0.6% | +4.1% | +4.9% | +0.4% | +1.3% | 4.23% |
| MBB | -0.2% | +0.4% | +3.9% | +4.7% | +0.3% | +1.2% | 4.33% |
Total returns including dividends, from adjusted daily closes as of 2026-08-07. 3Y/5Y/10Y are annualized. Yield is trailing-12-month distributions over the last close. Past performance does not predict future results.
Project the growth of $10,000 in VMBS vs MBB →
Shared Holdings(1212)
The top 10 shared positions account for 12% of the overlap, led by Government National Mortgage Association, Ginnie Mae and Uniform Mortgage-Backed Securities.
| Government National Mortgage Association | 0.32% | 0.55% | 0.32% |
|---|---|---|---|
| Ginnie Mae | 0.29% | 0.95% | 0.29% |
| Uniform Mortgage-Backed Securities | 0.26% | 1.05% | 0.26% |
| Uniform Mortgage-Backed Security, TBA | 0.20% | 0.34% | 0.20% |
| Freddie Mac Pool | 0.20% | 0.22% | 0.20% |
| Government National Mortgage Association | 0.20% | 0.31% | 0.20% |
| Uniform Mortgage-Backed Securities | 0.18% | 0.30% | 0.18% |
| Uniform Mortgage-Backed Securities | 0.16% | 0.24% | 0.16% |
| Government National Mortgage Association | 0.16% | 0.20% | 0.16% |
| Ginnie Mae | 0.15% | 0.67% | 0.15% |
| Uniform Mortgage-Backed Security, TBA | 0.15% | 0.83% | 0.15% |
| Uniform Mortgage-Backed Securities | 0.18% | 0.15% | 0.15% |
| Uniform Mortgage-Backed Securities | 0.15% | 0.31% | 0.15% |
| Government National Mortgage Association | 0.28% | 0.15% | 0.15% |
| Government National Mortgage Association | 0.14% | 0.27% | 0.14% |
| Uniform Mortgage-Backed Security, TBA | 0.14% | 0.64% | 0.14% |
| Government National Mortgage Association | 0.14% | 0.22% | 0.14% |
| Government National Mortgage Association | 0.13% | 0.28% | 0.13% |
| Government National Mortgage Association | 0.14% | 0.13% | 0.13% |
| Uniform Mortgage-Backed Securities | 0.13% | 0.17% | 0.13% |
| Government National Mortgage Association | 0.12% | 0.30% | 0.12% |
| Ginnie Mae II Pool | 0.12% | 0.15% | 0.12% |
| Government National Mortgage Association | 0.12% | 0.45% | 0.12% |
| Uniform Mortgage-Backed Securities | 0.23% | 0.12% | 0.12% |
| Government National Mortgage Association | 0.12% | 0.41% | 0.12% |
Showing the top 250 of 1212 shared holdings by overlap weight.
Frequently Asked Questions
How much do VMBS and MBB overlap?
VMBS and MBB overlap by 17.2% of portfolio weight. They share 1212 holdings (VMBS holds 5112 positions and MBB holds 11144), based on each fund's latest SEC-reported holdings.
Is it redundant to own both VMBS and MBB?
The two portfolios are 17.2% identical by weight. Owning both is not redundant. Most of each portfolio is distinct, so the funds can serve different roles.
What are the biggest shared holdings of VMBS and MBB?
The largest positions held by both funds are Government National Mortgage Association, Ginnie Mae, Uniform Mortgage-Backed Securities, Uniform Mortgage-Backed Security, TBA and Freddie Mac Pool. Together the top 10 shared positions account for 12% of the total overlap.
What does VMBS own that MBB doesn't?
3900 positions (65.8% of VMBS) are unique to VMBS, led by G2SF 5.5 7/26, FN CC2762 and FR SD4155. In the other direction, 9932 positions (66.2% of MBB) are unique to MBB.