Prepayment Risk

What Is Prepayment Risk?

Prepayment risk is the possibility that the principal of a loan or loan-backed security is repaid sooner than expected. It is most often discussed for mortgage-backed securities, where homeowners can pay off or refinance their mortgages before the due date. For the investor, an early repayment means the expected stream of interest income ends sooner than planned, and the returned principal must be put to work somewhere else.

How It Works

Most borrowers have the right to repay early without a penalty, and they tend to do so when conditions favor it. The most common trigger is a fall in interest rates. When market rates drop, homeowners may refinance into a new loan at a lower rate, which pays off the old loan in full. Investors who hold the older security then receive their money back just as rates have fallen, so they must reinvest at the new, lower yields. This is sometimes called reinvestment risk, and it is the main cost of prepayment risk.

Other factors also matter, such as home sales, which trigger payoffs regardless of rates, and borrower behavior that changes over time. Because prepayments are hard to predict, analysts estimate them using models based on historical patterns and assumed speeds, and they are stated as a percentage of the remaining balance paid each period.

Why It Matters to Investors

Prepayment risk affects the value and timing of returns, not just the total amount received. Securities with heavy prepayment risk often have uneven cash flows, which makes their yield harder to compare with other investments. When rates rise instead, prepayments slow down and the security's life extends, a related effect called extension risk. Together, these two effects are why mortgage-backed securities are often analyzed with specialized tools rather than simple maturity dates.