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Extra Mortgage Payment Calculator
Model recurring and one-time principal payments together, then compare the full payoff schedule.
Primary estimateLive · USD
Estimated result
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Based on the assumptions entered.
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Scenario comparison
Longer bars represent the larger value.
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What this result means
Extra principal reduces the balance earlier, so later interest is calculated on less principal. Monthly, annual, and one-time extras can be combined in one schedule.
How this calculator works
For every month, interest equals opening balance times annual rate divided by 12. Scheduled principal and all applicable extra payments reduce the balance, without rounding intermediate values.
Worked example
For example, add $200 every month, one extra scheduled payment each year, or a one-time principal payment. The calculator combines the events in the selected start month and shows both months saved and interest avoided.
Assumptions and limitations
- Extras are applied to principal with no penalty
- Annual extras recur every 12 months from the start month
- The one-time extra is applied in the start month
- Required payment remains unchanged
Frequently asked questions
How much can one extra mortgage payment per year save?
Savings depend on balance, rate, remaining term, and when the extra payment starts. Enter an annual extra equal to one scheduled payment to calculate the specific interest and payoff impact.
Is one extra payment per year the same as biweekly payments?
It can create a similar annual principal amount, but timing differs. Finly models one additional scheduled payment in the chosen start month.
Do extra mortgage payments lower the monthly payment?
Usually no. Principal-only extras normally shorten the payoff and reduce interest while the required payment stays unchanged. A lender-approved recast is a separate process that can lower the required payment.
Should extra mortgage payments be marked principal-only?
Yes, when your servicer supports that instruction. Confirm the payment was applied to principal and review any prepayment restrictions.
What if an extra payment exceeds the final balance?
The calculator caps the final payment at the remaining balance plus interest.
Sources and methodology
See the official primary source used for this calculator and read Finly’s calculation methodology.
Updated and logic reviewed: September 17, 2026. Results are educational estimates, not financial, tax, legal, or investment advice.