Risk that mortgage principal returns sooner than assumed, shortening investor cash flow and creating reinvestment risk.
Prepayment risk is the risk that mortgage principal returns sooner than an investor assumed because borrowers refinance, sell, curtail principal, or otherwise pay loans ahead of schedule.
Prepayment risk matters because homeowners can generally repay mortgage principal before the original schedule ends. That flexibility is valuable to borrowers, but it shortens the period over which investors receive interest and forces them to reinvest returned principal at then-current market rates.
The risk is especially important when investors buy a premium MBS above par. If principal returns quickly, part of the premium may not be recovered through future interest. Investor expectations about that behavior affect MBS prices and, indirectly, the market behind borrower rate sheets.
Prepayment risk is sometimes called contraction risk because faster principal return contracts the security’s expected life. It is paired with Extension Risk, which arises when principal returns more slowly than expected.
Borrowers rarely see prepayment risk named during application. They experience the borrower side when they refinance, sell, make principal curtailments, or pay off the mortgage early.
The term becomes useful when explaining why mortgage rates and rate locks are connected to a bond market that cares about how long loans are likely to remain outstanding. A borrower’s contractual right to prepay and an investor’s exposure to that choice are two sides of the same mortgage feature.
| Borrower action | Investor cash-flow effect |
|---|---|
| Refinance after rates fall | Existing loan may pay off earlier than expected |
| Sell the home | Mortgage may be paid off through sale proceeds |
| Make extra principal payments | Balance falls faster than scheduled |
| Full payoff from another source | Remaining principal returns immediately |
| Market path | Common borrower response | Main MBS concern |
|---|---|---|
| Mortgage rates fall materially | More borrowers can benefit from refinancing | Faster prepayment and reinvestment at lower yields |
| Mortgage rates remain near existing note rates | Refinance incentive may be limited | Turnover and ordinary curtailments drive more of the speed |
| Mortgage rates rise materially | Fewer borrowers refinance | Slower prepayment and greater extension risk |
These are tendencies, not guarantees. Home sales, credit eligibility, loan size, transaction costs, geography, and borrower circumstances can produce different behavior.
| Term | What it helps describe |
|---|---|
| Conditional Prepayment Rate | Annualized prepayment speed |
| Single Monthly Mortality | Monthly prepayment speed |
| PSA Prepayment Model | Benchmark convention for comparing assumed speeds |
| Average Life | Expected timing of principal return |
An investor pays 102 for an MBS with $1 million of current principal, a $20,000 premium over par. Rates fall and borrowers refinance much faster than expected, returning a large amount of principal at par before enough future interest has been collected to offset the premium.
The exact investment result depends on timing and cash flows, but the unrecovered premium illustrates why early payoff can hurt an investor even though receiving principal sounds favorable.
Prepayment risk differs from Extension Risk because prepayment risk is about loans paying off too quickly for investor expectations, while extension risk is about loans staying outstanding longer than expected.
It also differs from Prepayment Penalty. Prepayment risk is an investor cash-flow risk; a prepayment penalty is a loan term that may charge the borrower for early payoff in limited situations.
It differs from scheduled Amortization. Scheduled principal follows the payment plan, while prepayment is principal returned ahead of that plan. Security disclosures and models determine how curtailments, liquidations, and other unscheduled principal are classified.