Mortgage Payoff Calculator (2a) Extra Monthly Payments Who This Calculator is For: Borrowers who want an amortization schedule, or want to know when their loan will pay off, and how much interest they will save, if they make extra voluntary payments in addition to their required monthly payment. What This Calculator Does:This calculator provides amortization schedules for mortgages, with or without additional payments. If additional payments are made, interest savings and reduction in length of loan are calculated.