Extra mortgage payment calculator

What can an extra mortgage payment change?

An extra principal payment reduces the balance used to calculate later interest. This calculator compares your current contractual principal-and-interest payment with the same payment plus a recurring extra amount. It estimates future interest and payment counts from your current principal balance, without reconstructing your original loan or assuming a remaining term.

Use the mortgage payment calculator to estimate payments and selected housing costs for a proposed purchase. Use the mortgage amortization calculator for an original-loan, term-based schedule. This comparison instead answers what recurring extra principal might change on your current loan; it does not determine an affordable purchase price.

Find principal and interest on your statement

Your total mortgage payment may also contain property taxes, homeowners insurance, PMI or escrow. Those amounts do not repay principal. Use the contractual principal and interest (P&I) component, excluding existing extra payments. The calculator cannot detect whether an entered amount includes escrow, and it does not subtract assumed expenses.

For a hypothetical statement consisting only of $2,000 P&I and $500 escrow, the total is $2,500, but the input here is $2,000. Other statements may include additional components. If the P&I amount is unclear, ask your servicer before using the comparison. The CFPB’s payment-components explanation describes the distinction.

How the comparison works

The starting principal is modeled just after a regular payment, with the next payment one full month later. The annual note rate is divided by 100 and then 12. Each month, interest on the opening balance is rounded half up to the nearest cent. The regular payment covers that interest and then principal; extra principal is applied afterward at the same month-end, beginning with the next modeled payment.

The contractual P&I amount stays fixed. Each final regular payment and extra amount is capped so it cannot overpay the remaining obligation. Totals sum actual cent-ledger payments; “total paid” includes principal and interest only. Payoff duration is the number of monthly payments actually needed, rather than a calendar date or an assumed original term. Monthly cent rounding is this tool’s explicit model convention, not a claim about every lender’s accounting.

The baseline must repay on its own. A regular payment at or below the first month’s rounded interest is rejected, even if extra could make the loan amortize. A baseline taking more than 600 payments (50 years) is also unsupported. These are model boundaries, not lending rules. Dollar inputs allow up to two decimal places and $100 million; the fixed annual note rate allows 0–25% and up to six decimal places. Unsupported precision is rejected, not rounded silently.

Example: $200 extra each month

With $320,000 principal, 6% annual interest and $1,918.56 contractual monthly P&I, the baseline takes 361 payments, with $370,683.36 in future interest and $690,683.36 total paid. Adding $200 each month reduces this to 283 payments, $277,838.15 interest and $597,838.15 total paid: $92,845.21 interest saved and 78 months saved under this model. The final payments are $1.76 for the baseline and $404.23 with extra principal.

Why 361 rather than 360? The contractual payment is rounded to cents. After 360 payments of $1,918.56, $1.75 principal remains; the next month’s rounded interest adds $0.01, giving a final $1.76 payment. This calculator keeps your entered payment fixed instead of increasing payment 360 to force a 30-year finish. A lender’s handling can differ. The term-based amortization calculator uses a different final-payment convention and therefore may differ by a cent in total interest.

For a zero-interest example, a $1,000 balance with $83.33 regular P&I takes 13 payments, ending at $0.04. Adding $10 each month takes 11 payments, ending at $66.70. It saves two months but no interest. With zero extra, both schedules are identical.

Limits and a real payoff quote

This is projected monthly repayment, not a servicer payoff quote. The CFPB explains that a payoff amount may include interest through a specific date and fees beyond the current principal. Ask your servicer for a dated quote before paying off a loan.

The estimate excludes escrow, property tax, homeowners insurance, PMI, recasting, late fees and prepayment penalties. It does not model daily accrual, irregular first periods, missed payments, adjustable rates, lump sums, biweekly or irregular extra payments, interest-only periods or balloon obligations. Confirm how your servicer applies extra principal. Prepayment penalties depend on loan terms; do not assume every repayment strategy is penalty-free.

Interest saved is not a recommendation to prepay. This comparison does not assess your emergency savings, other debts, investment alternatives or tax circumstances.

Frequently asked questions

Educational estimate, not financial advice or a lender payoff quote. Assumes fixed monthly interest and extra principal applied after every regular payment. Actual servicing, accrued interest, fees and loan terms may differ. Check your statement and ask your servicer how to apply extra principal and obtain a dated payoff quote.