MBS measure showing how much of a mortgage pool's original principal remains outstanding.
Pool factor is a mortgage-backed securities measure showing the share of a mortgage pool’s original principal balance that is still outstanding.
Pool factor matters because mortgage pools shrink over time as borrowers make scheduled principal payments, refinance, sell, or pay extra principal. Investors use the factor to understand how much of the original pool remains.
For borrowers, the term is useful because it shows the pooled-market side of normal mortgage behavior. A borrower sees one monthly payment. The MBS market sees thousands of loans gradually reducing the pool balance.
Borrowers rarely see pool factor in their own mortgage documents. It appears after closing in secondary-market reporting, investor analysis, and MBS descriptions.
The term becomes practical when explaining how a Mortgage Pool changes after the loans begin amortizing and paying off.
| Pool factor direction | What it means |
|---|---|
| Near 1.000000 | Most of the original principal remains |
| Falling over time | Scheduled payments and prepayments are reducing the pool |
| Lower factor | Less principal remains for future cash flow |
A mortgage pool originally contained $100 million in loan principal. Later, $82 million remains outstanding. The pool factor shows that the current pool is smaller than the original pool because borrower payments and payoffs have reduced principal.
Pool factor differs from Mortgage Pool. The mortgage pool is the group of loans. Pool factor is a measurement of how much of that original pool remains.
It also differs from Prepayment Risk. Prepayment risk is the uncertainty that borrowers will pay off faster than expected. Pool factor is one way the resulting balance change shows up in pool reporting.
It also differs from Pass-Through Rate. Pass-through rate describes the investor cash-flow rate, while pool factor describes remaining principal.