Mortgage Overpayment Calculator

The baseline pays only the scheduled amount. The extra-payment plan adds your regular extra and each lump sum once, capped at the amount still owed. Both plans use the same rate and scheduled payment. Interest saved is baseline interest minus extra-plan interest; periods saved compares their last payment periods. A zero-rate loan of 120,000 over ten years requires 1,000 each month; adding 500 clears it in 80 months instead of 120.

Nominal monthly compounding gives period rate (1 + annual rate / 12)^(12 / payments per year) − 1. Nominal semiannual compounding gives (1 + annual rate / 2)^(2 / payments per year) − 1, commonly used for Canadian fixed-rate mortgages. Canadian lenders may use different conventions for variable-rate products. Choosing CAD does not choose a methodology or imply that either option matches every Canadian loan. At a 5% nominal semiannual rate, 100,000 amortized over 25 years has a modeled monthly payment of about 581.60.

Remaining amortization means the total payoff horizon, not the period until your rate renews. The entered rate is held constant beyond any fixed-rate term, so future renewal rates are not forecast. The period count is remaining years multiplied by 12 or 26, rounded to the nearest whole period. Every two weeks means 26 equal interest periods, with dates 14 days apart; it is not twice-monthly or an accelerated payment option. Monthly dates keep the starting day, clamped at month end. A lump sum is applied at the next scheduled payment on or after its date, after that period’s interest. This is not daily interest accounting.

The model excludes lender fees, early repayment charges, overpayment allowances, taxes, insurance, offset accounts and changing rates. No universal penalty-free allowance is assumed. Check your contract before making extra payments. Initial amortization is limited to 50 years, simulation to 100 years and lump sums to 20 entries; amounts are limited to one trillion and rates to 100%. Payment and balance calculations retain full precision, while display and CSV values are rounded. Currency changes display only.