What Is Single Monthly Mortality?

By Kristi Waterworth – Updated Jun 3, 2025 at 9:54 AM EST

Key Points

Single monthly mortality helps gauge MBS investment health by tracking premature loan payoffs.
Initial fast prepayment phase of an MBS is now shorter than in the 1980s, impacting profits.
Calculate single monthly mortality by comparing expected vs. actual payments, expressed as a percentage.

If you're considering becoming a mortgage-backed securities investor, there's a lot about mortgage lending that you might want to learn. Along with interest rates and how notes are engineered, it's important to be able to do calculations like the single monthly mortality rate. This figure can help you better understand what's happening with your investment.

Loading paragraph...

A hand holding a pen and writing in the loan amount on a mortgage application. — Image source: Getty Images.

Loading image...

Loading paragraph...

Related investing topics

Loading paragraph...

Investing in Mortgage REITs in 2026

Get tips on investing in real estate via mortgage REITs.

How to Calculate Accrued Interest

Learn to calculate accrued interest on loans or credit cards, considering rates, daily balances, and precision methods.

What You Need to Know About Active vs. Passive Investing

Some don't want to get in the weeds of investing, but others do. Each approach has its own investment style.

Loading hub_pages...

Loading paragraph...

About the Author

Kristi Waterworth has been a contributing real estate and financial expert at The Motley Fool, covering real estate, investing, and personal finance topics, since 2020. Kristi has been interviewed by various TV media outlets and podcasts for her real estate investing expertise – from residential real estate to digital real estate and everything in between. Kristi’s journalist career spans over 25 years, and she has written about real estate investing, homeownership, and home construction specifically for the last decade. She was also previously a licensed Realtor and general building contractor before the Great Recession and housing market collapse. She holds a bachelor’s degree in American history from Columbia College in Missouri.

TMFMaldivesBlue

@MaldivesBlues

The Motley Fool has a disclosure policy.