MBB vs SPY: Holdings Overlap
iShares · 11144 holdings · $39.1B · as of 2026-05-31
SPYState Street® SPDR® S&P 500® ETF Trust
State Street (SPDR) · 504 holdings · $812.0B · as of 2026-08-06
Holdings snapshots are 67 days apart (MBB: 2026-05-31, SPY: 2026-08-06). 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 MBB and SPY?
iShares MBS ETF (MBB, by iShares) holds 11144 positions; State Street® SPDR® S&P 500® ETF Trust (SPY, by State Street (SPDR)) holds 504. They have 0 holdings in common, and by portfolio weight the two funds are 0.0% identical. In practical terms the pair is essentially distinct, holding almost none of the same securities.
- Overlap by Weight
- 0.0%Sum of the smaller weight of each shared holding
- Shared Holdings
- 0MBB holds 11144 · SPY holds 504
- Weight in Shared Holdings
- MBB 0%·SPY 0%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 MBB
11144 of 11144 positions (98.1% of the fund) are not held by SPY. Showing the top 30 by weight.
- Freddie Mac Pool1.05%
- Ginnie Mae0.95%
- Uniform Mortgage-Backed Security, TBA0.83%
- Ginnie Mae0.67%
- Uniform Mortgage-Backed Security, TBA0.64%
- Ginnie Mae II Pool0.55%
Performance
| Fund | 1M | YTD | 1Y | 3Y (ann.) | 5Y (ann.) | 10Y (ann.) | Yield |
|---|---|---|---|---|---|---|---|
| MBB | -0.2% | +0.4% | +3.9% | +4.7% | +0.3% | +1.2% | 4.33% |
| SPY | +3.4% | +14.0% | +23.7% | +21.2% | +13.3% | +15.3% | 0.97% |
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 MBB vs SPY →
Shared Holdings(0)
These two funds have no holdings in common.
Frequently Asked Questions
How much do MBB and SPY overlap?
MBB and SPY overlap by 0.0% of portfolio weight. They share 0 holdings (MBB holds 11144 positions and SPY holds 504), based on each fund's latest SEC-reported holdings.
Is it redundant to own both MBB and SPY?
The two portfolios are 0.0% identical by weight. Owning both is genuine diversification: the funds hold almost none of the same securities.
What does MBB own that SPY doesn't?
11144 positions (98.1% of MBB) are unique to MBB, led by Freddie Mac Pool, Ginnie Mae and Uniform Mortgage-Backed Security, TBA. In the other direction, 504 positions (99.9% of SPY) are unique to SPY.