Mortgage Extra Payments Calculator — Save Interest & Pay Off Early
Enter your loan amount, rate, term and the extra amount you can afford each month — the calculator shows exactly how much interest you will save and how many years earlier you will be mortgage-free.
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Paid off 6 yrs 11 mo earlier
How does this calculator work?
Extra monthly payments go entirely to principal, so each month the balance is lower and less interest accrues. The calculator simulates the full amortisation with the extra amount and compares it to the base schedule — revealing months saved and total interest cut. Even $100/month extra on a 30-year loan can save tens of thousands.
Formula
How this is calculated
The calculator first solves the standard amortisation formula to find your fixed base monthly payment. It then runs two parallel month-by-month simulations. In the base scenario, each month a fixed share of the payment covers accrued interest (balance × monthly rate) and the rest reduces the principal. In the extra-payment scenario, the same process runs but with the extra amount added to every payment — the full extra reduces the outstanding principal immediately, so less interest accrues the following month.
The simulation for the extra-payment loan stops as soon as the balance reaches zero, which happens earlier than the original term. The difference in months is the time saved; the difference in cumulative interest is your saving.
The result assumes the extra payment is applied entirely to the principal (not held as a future payment credit), which is standard with most lenders. Check whether your lender allows unlimited penalty-free overpayments — some cap annual overpayments at 10% of the outstanding balance.
Frequently asked questions
Monthly extra payments save slightly more interest because the principal is reduced earlier each year, limiting the interest that accrues. A single annual lump-sum still saves substantial interest compared to no extra payments at all.
Most standard mortgages do, but some fixed-rate deals, especially in the UK and Canada, cap penalty-free overpayments (commonly 10% of the balance per year). Exceeding the cap triggers a prepayment penalty — check your mortgage contract first.
Even a few years of overpayments reduce your principal significantly. Use the amortisation calculator to see the remaining balance after that period, then re-run this calculator with that balance as the new starting amount.
Also known as
TG we-Calculate Editorial Team. (2026). Mortgage Extra Payments Calculator — Save Interest & Pay Off Early [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/mortgage-extra-payments-calculator
TG we-Calculate Editorial Team. "Mortgage Extra Payments Calculator — Save Interest & Pay Off Early." TG we-Calculate. 2026. https://we-calculate.com/calculator/mortgage-extra-payments-calculator.
TG we-Calculate Editorial Team, "Mortgage Extra Payments Calculator — Save Interest & Pay Off Early," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/mortgage-extra-payments-calculator
@misc{wecalculate_mortgage_extra_payments_calculator, title = {Mortgage Extra Payments Calculator — Save Interest & Pay Off Early}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/mortgage-extra-payments-calculator}}, year = {2026}, note = {TG we-Calculate} }
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