IUSB vs VMBS: Holdings Overlap
IUSBiShares Core Universal USD Bond ETF
iShares · 17783 holdings · $43.2B · as of 2026-04-30
VMBSVanguard Mortgage-backed Securities Index Fund
Vanguard · 5112 holdings · $15.6B · as of 2026-05-31
Holdings snapshots are 31 days apart (IUSB: 2026-04-30, VMBS: 2026-05-31). Weights and index membership change between snapshots, so the true current overlap is typically higher than shown. For funds tracking the same index, the gap can be 5–15 points.
How similar are IUSB and VMBS?
iShares Core Universal USD Bond ETF (IUSB, by iShares) holds 17783 positions; Vanguard Mortgage-backed Securities Index Fund (VMBS, by Vanguard) holds 5112. They have 374 holdings in common, and by portfolio weight the two funds are 4.9% identical. In practical terms the pair is essentially distinct, holding almost none of the same securities.
- Overlap by Weight
- 4.9%Sum of the smaller weight of each shared holding
- Shared Holdings
- 374IUSB holds 17783 · VMBS holds 5112
- Weight in Shared Holdings
- IUSB 6%·VMBS 17%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 IUSB
17409 of 17783 positions (92.8% of the fund) are not held by VMBS. Showing the top 30 by weight.
- U.S. Treasury Notes0.37%
- U.S. Treasury Notes0.37%
- U.S. Treasury Notes0.37%
- U.S. Treasury Notes0.37%
- U.S. Treasury Notes0.36%
- U.S. Treasury Notes0.36%
Only in VMBS
4738 of 5112 positions (82.8% of the fund) are not held by IUSB. Showing the top 30 by weight.
- Uniform Mortgage-Backed Security, TBA0.52%
- G2SF 5.5 7/260.36%
- Ginnie Mae II Pool0.31%
- FN CC27620.29%
- Ginnie Mae0.29%
- FR SD41550.27%
Performance
| Fund | 1M | YTD | 1Y | 3Y (ann.) | 5Y (ann.) | 10Y (ann.) | Yield |
|---|---|---|---|---|---|---|---|
| IUSB | -0.2% | +0.3% | +2.8% | +4.7% | +0.2% | +1.8% | 4.28% |
| VMBS | -0.1% | +0.6% | +4.1% | +4.9% | +0.4% | +1.3% | 4.23% |
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 IUSB vs VMBS →
Shared Holdings(374)
The top 10 shared positions account for 19% of the overlap, led by Government National Mortgage Association, Uniform Mortgage-Backed Securities and Government National Mortgage Association.
| Government National Mortgage Association | 0.11% | 0.12% | 0.11% |
|---|---|---|---|
| Uniform Mortgage-Backed Securities | 0.13% | 0.11% | 0.11% |
| Government National Mortgage Association | 0.21% | 0.10% | 0.10% |
| Government National Mortgage Association | 0.10% | 0.12% | 0.10% |
| Uniform Mortgage-Backed Securities | 0.10% | 0.13% | 0.10% |
| Government National Mortgage Association | 0.09% | 0.32% | 0.09% |
| Uniform Mortgage-Backed Securities | 0.09% | 0.14% | 0.09% |
| Uniform Mortgage-Backed Securities | 0.09% | 0.10% | 0.09% |
| Government National Mortgage Association | 0.09% | 0.14% | 0.09% |
| Uniform Mortgage-Backed Securities | 0.08% | 0.15% | 0.08% |
| Government National Mortgage Association | 0.08% | 0.08% | 0.08% |
| Government National Mortgage Association | 0.08% | 0.09% | 0.08% |
| Government National Mortgage Association | 0.08% | 0.10% | 0.08% |
| Uniform Mortgage-Backed Securities | 0.10% | 0.07% | 0.07% |
| Government National Mortgage Association | 0.07% | 0.14% | 0.07% |
| Government National Mortgage Association | 0.08% | 0.07% | 0.07% |
| Government National Mortgage Association | 0.07% | 0.08% | 0.07% |
| Government National Mortgage Association | 0.06% | 0.18% | 0.06% |
| Government National Mortgage Association | 0.06% | 0.16% | 0.06% |
| Government National Mortgage Association | 0.06% | 0.14% | 0.06% |
| Government National Mortgage Association | 0.05% | 0.09% | 0.05% |
| Uniform Mortgage-Backed Securities | 0.05% | 0.16% | 0.05% |
| Uniform Mortgage-Backed Securities | 0.05% | 0.11% | 0.05% |
| Uniform Mortgage-Backed Securities | 0.05% | 0.09% | 0.05% |
| Government National Mortgage Association | 0.05% | 0.10% | 0.05% |
Showing the top 250 of 374 shared holdings by overlap weight.
Frequently Asked Questions
How much do IUSB and VMBS overlap?
IUSB and VMBS overlap by 4.9% of portfolio weight. They share 374 holdings (IUSB holds 17783 positions and VMBS holds 5112), based on each fund's latest SEC-reported holdings.
Is it redundant to own both IUSB and VMBS?
The two portfolios are 4.9% identical by weight. Owning both is genuine diversification: the funds hold almost none of the same securities.
What are the biggest shared holdings of IUSB and VMBS?
The largest positions held by both funds are Government National Mortgage Association, Uniform Mortgage-Backed Securities, Government National Mortgage Association, Government National Mortgage Association and Uniform Mortgage-Backed Securities. Together the top 10 shared positions account for 19% of the total overlap.
What does IUSB own that VMBS doesn't?
17409 positions (92.8% of IUSB) are unique to IUSB, led by U.S. Treasury Notes, U.S. Treasury Notes and U.S. Treasury Notes. In the other direction, 4738 positions (82.8% of VMBS) are unique to VMBS.