Amortization Schedule Calculator

Builds an estimated month-by-month schedule for a fully amortizing, fixed-rate loan. Each row separates the scheduled payment into interest and principal, updates the remaining balance, and can model one equal extra principal payment every month.

Enter the amount borrowed, a nominal annual interest rate, a term that converts to a whole number of months, and any recurring extra amount. Use one currency consistently, then compare the displayed schedule with the payment terms in your lender's documents.

For 135,000 at 4.5% over 30 years with no extra payment, the estimated monthly principal-and-interest payment is 684.03. Month one contains 506.25 interest, about 177.78 principal, and a remaining balance near 134,822.22; automated tests cover this Freddie Mac example.

For principal L, monthly rate r and n payments, the regular payment is L × r ÷ [1 − (1 + r)^−n]. Each month the calculator finds interest as current balance × r, applies the rest of the payment plus the entered extra amount to principal, and reduces the final payment to the amount actually due. At 0% interest, principal is divided evenly across the months.

The model assumes a constant rate, monthly compounding, payments made on schedule at equal monthly intervals, and immediate application of every extra amount to principal. It does not model daily interest, changing rates, interest-only periods, balloons, skipped or late payments, recasting, or lender-specific rounding.

The fields are currency-neutral: 300,000 can mean dollars, euros, lira, or another unit, but every monetary input and output must use the same unit. The annual rate is treated as a nominal rate divided by 12, not necessarily a jurisdiction's APR, effective annual rate, tax treatment, or required disclosure method.

Results include principal and calculated interest only. Fees, points, taxes, insurance, escrow, mortgage insurance, penalties, and exchange-rate effects are excluded. Before relying on the extra-payment estimate, confirm that the contract permits prepayment and that the servicer will apply the amount to principal.

This is an educational estimate, not financial, credit, tax, or legal advice or a lender payoff statement. The method and explanation were checked against Consumer Financial Protection Bureau mortgage guidance and Freddie Mac's Understanding Amortization example; reviewed September 2026. Calculation runs locally in the browser, and Quiklio does not upload the entered values. Verify decisions with the contract, lender, and a qualified professional.