Understanding Agency Mortgage-Backed Securities (Agency MBS)
The housing market plays an integral role in the US economy, historically contributing around 15%-18% to annual GDP. Underpinning the U.S. residential housing market are 30-year fixed-rate mortgages, the vast majority of which are guaranteed by one of three government agencies. These mortgages form the basis for a major global fixed income sector: agency MBS.
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What are Agency Mortgage-Backed Securities?
Mortgage-backed securities are collections of residential mortgages with similar characteristics that are packaged together, or securitised, and sold to investors. The cash flows (principal and interest payments) from the underlying mortgage loans are passed through to investors.
Agency MBS are issued or guaranteed by one of three government or quasi-government agencies: Fannie Mae, Freddie Mac, and Ginnie Mae.
Why Janus Henderson for Agency MBS?
We believe much of the value in active bond asset management comes from security selection. Characteristics of individual securities can vary widely, and it is the role of the asset manager – ideally armed with decades of experience and sophisticated analytic systems – to pick securities that offer better risk-reward potential and combine them into a portfolio with the yield and risk targets investors seek.
We offer access to the growing and diverse securitised market through our full coverage products.
€51B
Firmwide securitised assets (as of 30/06/25)
Source: Janus Henderson Investors as of 30 June 2025.
Note: Firmwide assets include securitised products available outside of Europe and securitised portions of other fixed income strategies.
Dedicated MBS expertise
Global Head of Securitised Products | Portfolio Manager
Head of Structured and Quantitative Fixed Income | Portfolio Manager
Portfolio Manager | Securitised Analyst
Client Portfolio Manager
Key characteristics of Agency MBS
1
Strong credit ratings
Due to their government guarantee, all agency MBS carry the US government’s AA+ credit rating. Therefore, the risk of principal loss is negligible.
2
Improved absolute returns versus U.S. Treasuries
On an absolute basis, agency MBS have outperformed US Treasury bonds over longer investment horizons due to their earning an additional yield, or spread, over Treasuries.
3
Defensiveness
In times of market stress, higher-rated, long-duration bonds such as agency MBS tend to outperform as investors seek safety. Agency MBS was, in fact, one of the best-performing asset classes through the Global Financial Crisis, with the Bloomberg US MBS Index recording annual returns of +6.9%, +8.4%, and +5.9% in 2007, 2008, and 2009, respectively.
4
Low correlation to equities
MBS have historically exhibited very low correlation to equities, making them a good diversifier for multi-asset portfolios.
5
Diversification of risk exposures
While government and corporate bonds expose investors to a single borrower, agency MBS are made up of millions of individual mortgages, providing investors with a high degree of borrower diversification.
Risk considerations for agency MBS
Prepayment risk is the primary fundamental risk for agency MBS, as borrowers may pay off or refinance their mortgage at any point, which would negate the future income on that mortgage. The uncertainty about when, or if, a borrower will prepay a mortgage is known as prepayment risk. MBS pay an additional yield, or spread, above the yield on a comparable US Treasury to compensate investors for this risk.
Other risks affecting agency MBS include sensitivity to changes in interest rates, sensitivity to interest rate volatility, and changes in supply and demand.