IUSB vs MBB: Holdings Overlap
IUSBiShares Core Universal USD Bond ETF
iShares · 17783 holdings · $43.2B · as of 2026-04-30
iShares · 11144 holdings · $39.1B · as of 2026-05-31
Holdings snapshots are 31 days apart (IUSB: 2026-04-30, MBB: 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 MBB?
iShares Core Universal USD Bond ETF (IUSB, by iShares) holds 17783 positions; iShares MBS ETF (MBB, by iShares) holds 11144. They have 1203 holdings in common, and by portfolio weight the two funds are 10.4% identical. In practical terms the pair is lightly overlapping, with most of each portfolio distinct.
- Overlap by Weight
- 10.4%Sum of the smaller weight of each shared holding
- Shared Holdings
- 1203IUSB holds 17783 · MBB holds 11144
- Weight in Shared Holdings
- IUSB 12%·MBB 43%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
16580 of 17783 positions (86.4% of the fund) are not held by MBB. 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 MBB
9941 of 11144 positions (55.5% of the fund) are not held by IUSB. Showing the top 30 by weight.
- Ginnie Mae0.95%
- Uniform Mortgage-Backed Security, TBA0.83%
- Ginnie Mae0.67%
- Uniform Mortgage-Backed Security, TBA0.64%
- Ginnie Mae0.46%
- Ginnie Mae II Pool0.36%
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% |
| 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 IUSB vs MBB →
Shared Holdings(1203)
The top 10 shared positions account for 10% of the overlap, led by Government National Mortgage Association, Government National Mortgage Association and Uniform Mortgage-Backed Securities.
| Government National Mortgage Association | 0.21% | 0.16% | 0.16% |
|---|---|---|---|
| Government National Mortgage Association | 0.11% | 0.30% | 0.11% |
| Uniform Mortgage-Backed Securities | 0.10% | 0.12% | 0.10% |
| Uniform Mortgage-Backed Securities | 0.10% | 0.33% | 0.10% |
| Government National Mortgage Association | 0.10% | 0.41% | 0.10% |
| Uniform Mortgage-Backed Securities | 0.10% | 0.17% | 0.10% |
| Uniform Mortgage-Backed Securities | 0.10% | 0.18% | 0.10% |
| Government National Mortgage Association | 0.09% | 0.55% | 0.09% |
| Government National Mortgage Association | 0.09% | 0.53% | 0.09% |
| Uniform Mortgage-Backed Securities | 0.09% | 0.13% | 0.09% |
| Government National Mortgage Association | 0.09% | 0.13% | 0.09% |
| Uniform Mortgage-Backed Securities | 0.08% | 0.44% | 0.08% |
| Government National Mortgage Association | 0.08% | 0.28% | 0.08% |
| Uniform Mortgage-Backed Securities | 0.08% | 0.31% | 0.08% |
| Government National Mortgage Association | 0.08% | 0.54% | 0.08% |
| Government National Mortgage Association | 0.08% | 0.11% | 0.08% |
| Uniform Mortgage-Backed Securities | 0.08% | 0.07% | 0.07% |
| Government National Mortgage Association | 0.07% | 0.13% | 0.07% |
| Government National Mortgage Association | 0.07% | 0.27% | 0.07% |
| Government National Mortgage Association | 0.07% | 0.19% | 0.07% |
| Uniform Mortgage-Backed Securities | 0.07% | 0.12% | 0.07% |
| Government National Mortgage Association | 0.06% | 0.28% | 0.06% |
| Government National Mortgage Association | 0.06% | 0.12% | 0.06% |
| Government National Mortgage Association | 0.06% | 0.20% | 0.06% |
| Government National Mortgage Association | 0.06% | 0.09% | 0.06% |
Showing the top 250 of 1203 shared holdings by overlap weight.
Frequently Asked Questions
How much do IUSB and MBB overlap?
IUSB and MBB overlap by 10.4% of portfolio weight. They share 1203 holdings (IUSB holds 17783 positions and MBB holds 11144), based on each fund's latest SEC-reported holdings.
Is it redundant to own both IUSB and MBB?
The two portfolios are 10.4% 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 IUSB and MBB?
The largest positions held by both funds are Government National Mortgage Association, Government National Mortgage Association, Uniform Mortgage-Backed Securities, Uniform Mortgage-Backed Securities and Government National Mortgage Association. Together the top 10 shared positions account for 10% of the total overlap.
What does IUSB own that MBB doesn't?
16580 positions (86.4% 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, 9941 positions (55.5% of MBB) are unique to MBB.