Finance term
Mortgage-Backed Security (MBS)
Also known as: MBS, agency MBS, non-agency MBS, pass-through certificate
Definition
A mortgage-backed security (MBS) is a bond backed by a pool of residential or commercial mortgages — investors receive a pass-through of borrower principal and interest payments. Agency MBS are issued or guaranteed by Ginnie Mae, Fannie Mae, or Freddie Mac; the Federal Reserve tracks MBS holdings on its H.8 statistical release.
Detailed explanation
MBS are the largest segment of the U.S. fixed-income market. Lenders originate mortgages, pool them, and issue securities backed by the monthly principal and interest payments from borrowers. Two categories exist: (1) Agency MBS — guaranteed by government-sponsored enterprises (GSEs) Fannie Mae (FNMA) and Freddie Mac (FHLMC) or by Ginnie Mae (GNMA), which carries the full faith and credit of the U.S. government. (2) Non-agency MBS — privately issued, no government guarantee, higher yield but higher credit risk.
The Federal Reserve publishes MBS holdings data on its H.8 Assets and Liabilities of Commercial Banks statistical release (federalreserve.gov/releases/h8/). The Fed's large-scale purchases of agency MBS (quantitative easing) during 2008–2014 and 2020–2022 directly suppressed mortgage rates. When the Fed reduces its MBS balance sheet (quantitative tightening), mortgage rates rise as private investors demand higher yields to absorb supply.
For business borrowers, MBS market dynamics matter when financing commercial real estate. CMBS (Commercial Mortgage-Backed Securities) pricing benchmarks against agency MBS spreads. Rising MBS spreads translate directly into higher commercial real estate loan rates, affecting refinancing and acquisition economics.
◈ Worked example
- A bank pools 1,000 conforming 30-year fixed mortgages meeting Fannie Mae guidelines, sells them to Fannie, which issues an agency MBS pass-through certificate to investors — freeing the bank's capital to originate new loans.
- Federal Reserve H.8 release (Mar 2025): Commercial banks held approximately $2.5 trillion in MBS on their balance sheets, making MBS the single largest asset category for the banking system.
- Non-agency MBS: A private label securitization pools jumbo mortgages exceeding conforming loan limits. No GSE guarantee — credit enhancement via tranching (senior AAA, subordinate BB) structures the risk profile instead.
Common questions
The most-asked questions about Mortgage-Backed Security (MBS) — answered straightforwardly.
Why do MBS affect mortgage rates for business owners? +
When investors demand higher yields to buy MBS (due to Fed tightening or market uncertainty), lenders must offer higher mortgage rates to create loans that can be sold into the MBS market competitively. The 30-year fixed mortgage rate historically tracks the 10-year Treasury plus an MBS spread — when that spread widens, rates rise independently of Treasury moves.
What is the difference between Ginnie Mae, Fannie Mae, and Freddie Mac MBS? +
Ginnie Mae (GNMA) backs FHA and VA loans and carries an explicit U.S. government guarantee. Fannie Mae and Freddie Mac MBS carry an implied government backing (now in conservatorship since 2008) but not an explicit Treasury guarantee. All three are considered 'agency MBS' — lower yield than non-agency but near-zero credit risk for investors.
Further reading
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https://clearvaluelending.com/glossary/mortgage-backed-security