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ETF comparison

IUSB vs MBB

Both US Aggregate Bond.

iShares Core Universal USD Bond ETF · iShares MBS ETF

Holdings overlap

Weighted by ISIN/CUSIP
10.3 %

1,194 positions appear in both funds. Buying equal dollars of IUSB and MBB would leave roughly 10.3% of each dollar exposed to the same underlying securities.

IUSB only 91.0% Shared 10.3% MBB only 94.1%
In IUSB only
16,585 positions
Shared
1,194 positions
In MBB only
9,957 positions

Side by side

IUSB

iShares Core Universal USD Bond ETF

iShares · US Aggregate Bond

88 composite / 100
Expense ratio
0.060%
Net assets
$42.77B
TTM yield
4.26%
Top-10 conc.
6.7%
MBB

iShares MBS ETF

iShares · US Aggregate Bond

88 composite / 100
Expense ratio
0.040%
Net assets
$39.63B
TTM yield
4.30%
Top-10 conc.
11.7%

Sub-score comparison

94
Cost
96
52
Tax efficiency
52
100
Liquidity
100
100
Concentration
98
—
Tracking quality
—
IUSB sub-score MBB

Tracking quality isn't part of the composite — see what we don't score for why.

Cost difference

MBB is 2 bps cheaper than IUSB. On a $100,000 position that's about $20/yr more in fees for IUSB.

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 IUSB vs MBB.

Top shared holdings

1,194 shared in total
# Holding In IUSB In MBB Overlap
1 Government National Mortgage Association 0.21% 0.14% 0.14%
2 Government National Mortgage Association 0.11% 0.31% 0.11%
3 Federal Home Loan Mortgage Corp. 0.10% 0.12% 0.10%
4 Federal National Mortgage Association 0.10% 0.33% 0.10%
5 Government National Mortgage Association 0.10% 0.33% 0.10%
6 Federal National Mortgage Association 0.10% 0.17% 0.10%
7 Federal Home Loan Mortgage Corp. 0.10% 0.35% 0.10%
8 Government National Mortgage Association 0.09% 0.42% 0.09%
9 Government National Mortgage Association 0.09% 0.55% 0.09%
10 Federal National Mortgage Association 0.09% 0.14% 0.09%
11 Federal National Mortgage Association 0.08% 0.45% 0.08%
12 Government National Mortgage Association 0.08% 0.29% 0.08%

Only in IUSB

16,585 total
  • Blackrock Liquidity Tempcash 2.88%
  • United States of America 0.37%
  • United States of America 0.37%
  • United States of America 0.37%
  • United States of America 0.37%
  • United States of America 0.36%
  • United States of America 0.36%
  • United States of America 0.36%
  • United States of America 0.35%
  • United States of America 0.34%

Only in MBB

9,957 total
  • Government National Mortgage Association 1.00%
  • UMBS, TBA 0.57%
  • Government National Mortgage Association 0.53%
  • UMBS, TBA 0.50%
  • Government National Mortgage Association 0.45%
  • Government National Mortgage Association 0.37%
  • UMBS, TBA 0.35%
  • Fannie Mae 0.33%
  • Fannie Mae 0.29%
  • UMBS, TBA 0.25%

Open IUSB or MBB at a brokerage

Both funds trade commission-free at major US brokerages.

Open at Fidelity

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.