Mortgage Payoff Calculator (2e) Extra Monthly Payments and Property Value Appreciation to Reach a Desired Equity in a Specified Period Who This Calculator is For: Borrowers who want to know how much extra they must pay to reach a target equity position 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, given an assumed appreciation rate, to reach a targeted equity position within a specified period.