Prepayment Risk Explainer
Prepayment risk is the chance that a borrower returns principal earlier than the lender or investor expected. It is especially important in mortgages and mortgage-backed securities, but it also appears in callable debt and pools of auto, student, or other loans.
When interest rates fall, borrowers may refinance at lower costs. Home sales, relocations, defaults, loan seasoning, and borrower incentives also affect repayment. An investor who paid a premium can lose expected interest and may have to reinvest returned principal at lower market yields.
Prepayment changes both timing and valuation. Faster cash flow shortens duration, while slower prepayment when rates rise can extend duration and increase price declines. This asymmetry helps explain negative convexity in many mortgage-backed securities.
Models estimate prepayments using rates, loan age, borrower characteristics, geography, seasonality, housing turnover, and prior refinancing. Results remain uncertain because behavior and underwriting change. Investors should test fast and slow scenarios, understand tranche rules, and distinguish prepayment risk from credit losses, even though defaults can also return principal through liquidation.
Refinancing, sales, calls, and other events alter scheduled cash flow.
The investor may lose higher-yielding payments.
Falling rates can speed prepayment; rising rates can slow it.
Duration therefore changes.
Borrower incentives, loan age, and housing turnover are uncertain.
Scenario analysis is more useful than one forecast.
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