MBS timing measure estimating when principal is expected to be returned to investors.
Average life is a mortgage-backed securities timing measure estimating when principal is expected to be returned to investors.
Average life matters because mortgage investors care not only about how much principal is returned, but when it is returned. Mortgage principal can come back through scheduled amortization, refinancing, home sales, curtailments, and other payoffs.
For borrowers, the term explains why investor pricing is sensitive to refinance behavior and payoff timing. The borrower’s right or ability to repay early changes the expected life of mortgage cash flows.
Borrowers do not usually see average life in their own loan documents. It appears in MBS analytics, investor reports, and discussions of prepayment assumptions.
The term becomes practical when connecting borrower actions such as refinancing or selling the home to the market’s expectation about how long mortgage cash flows will last.
| Term | What it focuses on |
|---|---|
| Weighted Average Maturity | Scheduled remaining maturity |
| Average life | Expected timing of principal return |
| Prepayment Risk | Principal returning sooner than expected |
| Extension Risk | Principal staying outstanding longer than expected |
A pool may contain 30-year mortgages, but investors do not expect every loan to last exactly 30 years. Refinances, sales, and extra payments can return principal earlier, so the pool’s expected average life may be much shorter than the original final maturity.
Average life differs from Weighted Average Maturity because maturity is tied to scheduled final repayment, while average life estimates when principal is expected to come back.
It also differs from Pool Factor. Pool factor measures remaining principal at a point in time. Average life estimates timing across future principal payments.
It also differs from Conditional Prepayment Rate. CPR is a prepayment-speed assumption or measure, while average life is a timing result influenced by prepayment behavior.