PSA

A prepayment model based on an assumed rate of prepayment each month of the then unpaid principal balance of a pool of mortgages . PSA is used primarily to derive an implied prepayment speed of new production loans, a 100% PSA assumes a prepayment rate of 2% per month in the first month following the date of issue , increasing at 2% per month thereafter until the 30th month. Thereafter, 100% PSA is the same as 6% CPR.