Mortgage Extra Payment & Early Payoff Calculator

How much time and interest will extra mortgage payments save you? Start with your current fixed-rate mortgage balance, then compare extra principal payments or work backward from an earlier payoff goal.

Your existing mortgage

Principal and interest only. Property tax, insurance, HOA, PMI and escrow do not pay down your mortgage. The calculated payment from these loan details drives both plans; an entered payment is for comparison only.

Extra principal payments

Use any combination, or leave all extras blank for the baseline only. Monthly extra comes first, then annual extra, then a lump sum, capped at the remaining principal.

A lump sum dated on/before the next payment is modeled immediately before that payment's interest accrues. Later lump sums apply on the first scheduled payment date on/after the entered date. Annual extras apply once in the selected calendar month, starting with the first eligible payment.

How it works

The baseline required principal-and-interest payment comes from your current balance, fixed interest rate and remaining number of monthly payments. At 0% interest it is balance ÷ payments; otherwise it uses the standard fixed-rate amortization formula.

For each payment, monthly interest is beginning balance × APR ÷ 100 ÷ 12. Scheduled P&I pays interest first and then principal. Extra principal reduces the balance used for future interest, which can reduce both interest and time in debt. Extras are capped so the ending balance never becomes negative.

Your scheduled required P&I normally remains the same after an extra payment unless your loan is formally recast or refinanced. This calculator does not model recasting or refinancing. Target mode calculates the monthly P&I needed to repay the current balance over the shorter target period.

Assumptions and limitations

This is a planning estimate for an existing fixed-rate mortgage, using monthly interest, on-time payments and extra principal. Next Payment Date is payment 1, not a loan origination date. Later dates retain the original day-of-month, capped at month-end, without timezone conversion.

A lump sum before the first scheduled date is treated as principal prepaid before first interest, not as daily-interest accrual from its actual posting date. A lump sum after payoff is unused and creates no new payment. Annual extras start in the first eligible scheduled calendar month and stop at payoff.

Actual lender payoff may differ because of daily interest, posting dates, lender rounding, escrow, fees, recasting, late or deferred payments and servicing rules. Check how your lender applies extra principal and whether prepayment charges apply. This is not a lender payoff quote or financial advice. Tax, insurance, HOA, PMI and escrow are excluded. Supported horizons are 1–1,200 monthly payments; rates 0–100%.

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