CPR meaning conditional prepayment rate, that refers to the annualized percentage of the pre-existing mortgage pool expected to be prepaid in the year. It is the percentage of the outstanding amount of the security or the loan minus the scheduled payments. It is assumed the rate of prepayment will be a constant in conditions when a constant percentage of the mortgage is given. The factor CPR is dependent on the factors like the underlying pool, the future predictions and the historical prepayment rate. It is used for a variety of loans like mortgages, student loans, pass-through securities and others. It is mostly expressed as a percentage.