What Shapes the Agency Mortgage Portfolio of iShares MBS ETF (Nasdaq:MBB)?

Sonal Goyal

03 November 2026 04:40 PM AEDT

What Shapes the Agency Mortgage Portfolio of iShares MBS ETF (Nasdaq:MBB)?

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Highlights

MBB seeks exposure to US agency mortgage-backed securities.
The fund reports NAV of USD 91.80 as of 2 November 2026.
MBB lists an expense ratio of 0.04% and distributes monthly.

iShares MBS ETF (Nasdaq:MBB) seeks to track US agency mortgage-backed securities. Its NAV stood at USD 91.80 as of 2 November 2026. Net Assets totalled USD 35,829,112,112 as of 2 November 2026.

Agency Mortgage Cash Flows Drive the Structure

MBB tracks the Bloomberg U.S. MBS Index. The benchmark covers investment-grade mortgage-backed pass-through securities issued or guaranteed by US government agencies or sponsored entities. Eligible pools include securities associated with Ginnie Mae, Fannie Mae and Freddie Mac. The fund’s exposure is therefore shaped by mortgage cash flows and the structures used to hold them.

The fund uses representative sampling, selecting investments intended to resemble the benchmark’s overall characteristics. It may therefore hold a different collection of securities from the index while seeking a similar Investment profile.

Portfolio Composition and Exposure

MBB reported 10,833 holdings as of 30 October 2026. Its allocation by Market Value included Federal National Mortgage Association at 42.64%, Federal Home Loan Mortgage Corporation at 30.24% and Government National Mortgage Association at 24.01% as of 1 October 2026.

The portfolio’s effective duration was 5.72 yrs as of 30 October 2026. Weighted average Maturity was 7.58 yrs as of 30 October 2026.

Duration measures sensitivity to Interest Rate changes. Maturity describes the timing of principal repayments, while cash-flow patterns and embedded Options can make the two measures differ. These characteristics describe the bond portfolio rather than a fixed outcome for shareholders.

The fact sheet dated 30 September 2026 recorded Credit allocations including AA Rated at 99.48%. These classifications describe underlying securities at that date; ratings and portfolio credit quality can change.

Fees and Distribution Policy

The published expense ratio is 0.04%. Distributions are scheduled monthly.

The 30-day SEC Yield was 4.40% as of 30 October 2026. This standardised income measure reflects the fund’s recent income after expenses; it is separate from changes in the market value of its shares.

The prospectus notes that brokerage commissions and other intermediary charges may apply separately. Fund shares trade at market prices, which can differ from NAV, so the stated NAV does not establish the price of every exchange transaction.

Key Insights

Changes in mortgage repayments can shorten or extend the expected life of the securities. Interest rate moves and prepayment behaviour can influence both valuation and the timing of cash available for reinvestment.

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