The portion of the original loan amount represented by the periodic, equal debt service payments. The decimal factor that is applied to the original mortgage or deed-of-trust amount to find the level-payment, full-amortized mortgage debt service, payable each equal time period. This payment factor, usually quoted in decimal-fraction form, covers the repayment of principal and payment of interest each mortgage-payment period. There are many combinations of interest rate, loan term to maturity, and frequency of loan payment per year that may be represented by a single loan constant.

The yearly percentage of interest, which remains the same over the life of an amortized loan based on the monthly payment in relation to the principal originally loaned.

The annual payment required per dollar of a mortgage loan, including principal and interest.