MBSD vs SPMB

MBSDBNorthern Trust Disciplined Duration MBS ETF

SPMBAState Street SPDR Portfolio Mortgage Backed Bond ETF

In short

MBSD Agency mortgage bonds let their duration wander as homeowners refinance or sit tight. MBSD tracks an index built to keep that drift on a leash, offering mortgage-bond exposure with rate sensitivity set by rules instead of by the market's mood.

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

MBSD The fund is designed to provide market-like exposure to mortgage-backed securities while limiting duration drift through a rules-based index methodology.

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

• MBSD The whole point is duration discipline: a rules-based index designed to give market-like mortgage-bond exposure while limiting duration drift, so rate sensitivity is governed by methodology.flexshares.com
• Charges 0.21% a year, less than the typical fee in the MBS ETF group, and it has been running since 2014 rather than arriving as a recent idea.
• Spreads across roughly 500 mortgage bonds and pays monthly, so income lands on a mortgage-payment rhythm instead of twice a year.

• 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

• MBSD Thinly traded. Spreads and limit orders matter more here than with the category's household names.
• Duration control carries a price tag: VMBS, MBB and SPMB track the broad agency mortgage market for single-digit basis points.
• Constraining duration means it is not built to move like the full mortgage-backed market. That is the design, but it is a different exposure, not a copy.flexshares.com

• 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 MBSD profile⁠

Full SPMB profile⁠