Mortgage Payoff Calculator (2c) Extra Monthly Payments to Pay Off in Specified Period Who This Calculator is For: Borrowers who want to know how much extra they must pay, above their required monthly payment, to pay off their loan within a specified period. What This Calculator Does: This calculator shows the additional amount that must be paid on fixed-rate mortgages, above the required monthly payment, to pay off a loan within a specified period. It also displays the amortization schedule and the interest savings