MBB vs VMBS

MBBAiShares MBS ETF

VMBSAVanguard Mortgage-Backed Securities ETF

In short

MBB Launched in 2007, MBB is the plain-vanilla way to own U.S. agency mortgage bonds: one of the biggest and busiest funds in a small niche, tracking the Bloomberg U.S. MBS Index for four basis points.

VMBS The plumbing of the U.S. housing market in one ticker: pooled home loans from Ginnie, Fannie and Freddie, tracked by index for 0.03% a year, with income paid monthly.

Stated mandate

MBB The fund seeks to track an index composed of U.S. agency mortgage-backed securities.

VMBS The fund seeks moderate and sustainable current income by investing primarily in U.S. agency mortgage-backed pass-through securities issued by GNMA, FNMA, and FHLMC.

Why people hold it

• MBB Four basis points to rent the entire agency mortgage market, against a category median near 0.35%. In low-coupon bond land, that gap compounds quietly.
• Scale is the real feature: one of the largest and most actively traded funds in the mortgage-bond category, which generally shows up as tighter spreads.
• Pays monthly, and the mandate stays narrow: an index of U.S. agency mortgage-backed securities, nothing exotic bolted on.
• Among the stronger builds in a thin peer group of mortgage-bond ETFs, on the combination of cost, trading friction and issuer staying power.

• VMBS 0.03% a year is the cheap end of the mortgage-bond aisle: SPMB and MBB charge 0.04%, JMTG 0.24%, and the typical peer runs far higher.
• Agency pass-throughs from GNMA, FNMA and FHLMC. Credit isn't the main variable here; rates and mortgage behavior are.vanguard.com
• Trading since 2009, a multi-billion-dollar fund holding roughly 300 pools and paying monthly. Boring in the way bond ballast is supposed to be.
• Sits in the top quartile of its mortgage-bond peer group, one of the stronger builds in a crowded, look-alike category.

Worth knowing

• MBB This is one slice of the bond market. Agency mortgage paper only, with no Treasuries or corporates alongside it.
• Mortgage bonds cut both ways with rates: borrowers refinance when yields fall and sit tight when they rise, so the portfolio's duration shifts underneath you.
• On price it's a photo finish: SPMB tracks the same index at the same 0.04%, and VMBS runs a basis point cheaper.

• VMBS Mortgages don't keep a schedule. Homeowners refinance when rates fall, returning cash to reinvest at lower yields; when rates rise, payoffs slow and bonds stretch out.vanguard.com
• The mandate is current income from one slice of the bond market. No Treasuries, no corporates, no equity kicker.
• Share prices move with interest rates, so this behaves like a bond fund, not a cash parking spot.vanguard.com

Full MBB profile⁠

Full VMBS profile⁠