How much time and interest could an extra payment save you? This free extra mortgage payment calculator simulates your loan with and without an added monthly amount, showing exactly how many months and dollars it saves.
This is an estimate based on your current payment and rate remaining constant. Confirm your loan doesn’t have prepayment penalties before adding extra payments.
How Extra Mortgage Payment Calculator Works
Adding a fixed extra amount to your monthly mortgage payment reduces the principal balance faster than the scheduled amortization alone, which shortens the loan and cuts total interest. This calculator compares your loan’s payoff time and interest cost with and without the extra amount.
Formula: Remaining Months = −ln(1 − r×Balance÷Payment) ÷ ln(1+r), where r = Interest Rate ÷ 12 ÷ 100 — calculated once using the current payment, and again using (Current Payment + Extra), then compared
- Balance — the remaining loan balance today
- Rate — the loan’s current annual interest rate
- Payment — the current scheduled monthly payment
- Extra — the additional amount added to each monthly payment
Example Scenarios
| Balance | Rate | Payment | Extra | Time Saved | Interest Saved |
|---|---|---|---|---|---|
| $280,000 | 6.5% | $1,900 | $200 | ~59 months | ~$65,000 |
| $150,000 | 5.0% | $1,200 | $100 | ~19 months | ~$7,300 |
| $400,000 | 7.0% | $2,800 | $400 | ~84 months | ~$144,000 |
| $100,000 | 4.5% | $900 | $150 | ~26 months | ~$5,700 |
Extra Mortgage Payment Calculator FAQ
Why does a relatively small extra payment save so much interest?
Extra payments reduce principal immediately, and every dollar of principal removed early stops accruing interest for the rest of the loan term, so the savings compound the earlier the extra payments start.Should I confirm anything with my lender before adding extra payments?
Yes. Confirm your lender applies extra payments directly to principal (not to a future scheduled payment) and that the loan has no prepayment penalty, since both can change the actual benefit you receive.Does a bigger extra payment always save proportionally more?
Generally yes, since larger extra payments reduce principal faster, but the relationship isn’t perfectly linear — the savings depend on how early in the loan the extra payments start and how much interest remains to be avoided.Is it better to make one large extra payment or smaller ones every month?
Consistent monthly extra payments compound their principal-reducing effect earlier and more steadily than a single lump sum made later, generally producing more interest savings for the same total extra amount paid over time.Does this calculator assume the interest rate stays the same?
Yes. The projection assumes your current rate and payment remain constant throughout, which fits a fixed-rate mortgage; an adjustable-rate loan would need to be recalculated whenever the rate resets.Could extra payments affect anything besides interest and payoff time?
Extra payments build equity faster, which can help you reach the 20% equity threshold sooner if you’re paying PMI, in addition to the direct interest and time savings shown here.Related Calculators
Before deciding how much extra to add, it can help to recheck your full monthly payment breakdown or see your existing amortization schedule in detail.