MBBA vs SPMB

MBBACiShares Mortgage-Backed Securities Active ETF

SPMBAState Street SPDR Portfolio Mortgage Backed Bond ETF

In short

MBBA Active management aimed at the plumbing of the mortgage market: iShares gives a manager room to pick agency MBS instead of mirroring the Bloomberg U.S. MBS Index, and charges less than the typical fund in this corner to do it.

SPMB The no-frills way to own America's mortgage bonds. SPMB tracks the Bloomberg U.S. MBS Index for four basis points, a fraction of what the typical mortgage-bond ETF charges, and pays income monthly.

Stated mandate

MBBA The Fund seeks to maximize total return while generating income and applying prudent investment management.

SPMB The fund seeks to track, before fees and expenses, the price and yield performance of the Bloomberg U.S. MBS Index.

Why people hold it

• MBBA Runs at 0.25% a year, under the 0.35% typical of MBS funds in its group. Active mandates usually charge up from the index, not down toward it.
• The mandate: maximize total return while generating income. The Bloomberg U.S. MBS Index is the yardstick, not a leash the manager has to hug bond for bond.
• Spread across roughly 500 US mortgage bonds in a plain 1940 Act open-end fund. No K-1, no derivative wrapper, no offshore structure to decode.
• Fund inception dates to 1998, meaning this mortgage playbook was running long before most of the ETFs it now sits beside existed.

• SPMB Four basis points a year, against a 0.35% median for mortgage-bond ETFs. Cost is where this fund does its loudest talking.
• Runs the same Bloomberg U.S. MBS Index as iShares' MBB at the same 0.04% fee, and undercuts MBBA, which tracks that index for far more.
• Roughly 2,700 mortgage bonds in a single line item, inside a multi-billion-dollar fund that trades actively, with distributions paid monthly.
• Trading since 2009, and one of the strongest implementations in its mortgage-bond peer group.

Worth knowing

• MBBA Cheap for active, still pricier than the index route: MBB, VMBS and SPMB all sit at a few basis points. Here you are paying for a manager's calls.
• Because it is active, there is no tracking record to audit, and only a short window of risk history exists. Less to measure than a long-running tracker.
• Smaller and more lightly traded than the index heavyweights in the MBS category, which is where limit orders earn their keep.

• SPMB Homeowners refinance when rates fall, so mortgage bonds get paid back early and rally less than Treasuries. That quirk is built into the index, not the fund.
• Prices move with interest rates and the monthly payout floats with the portfolio. This is a bond fund, not a cash substitute.
• US mortgages only. No Treasuries, no corporates, no credit spice. A building block for a bond sleeve rather than the whole sleeve.

Full MBBA profile⁠

Full SPMB profile⁠