The mortgage payment formula to calculate a fixed monthly payment is P = L[c(1 + c)^n]/[(1 + c)n - 1]. In this formula, P stands for monthly payment, L is loan, c is the monthly rate and n refers to the month in which the balance is paid in full.
To calculate a balance when months are remaining on a loan, the equation B = L[(1 + c)n - (1 + c)p]/[(1 + c)n - 1] is used. In this equation, B is the balance, and p refers to the number of months left. To calculate annual percentage rate, the formula L - F = P1/(1 + i) + P2/(1 + i)2 +… (Pn + Bn)/(1 + i)n is used. In this instance, the variable i is internal rate of return, F refers to points and lender fees, and Bn refers to the balance in month n.