Measuring Prepayment Speeds: CPR, PSA, SMM — Mortgage ...

11/14/2016 · PSAs are quoted as percentages of the base model. For example, 250% PSA implies that for every month, the base model’s CPR is multiple by 2.5. (Since 100% PSA implies a 1.0% CPR in month 5, 250% PSA implies 2.5% CPR for that month.) The chart below illustrates prepayment speeds at different percentages of the PSA model for a newly-issued pool.