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Loan Overpayment Calculator — Save on Interest
The loan overpayment calculator shows exactly how much interest you will save by making an extra lump-sum payment toward your principal. Choose between shortening the remaining term (keeping the instalment) or reducing the monthly instalment (keeping the term), and compare both outcomes side by side.
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How we calculate the overpayment saving
We subtract the overpayment from the current balance to get a new balance S. The new annuity instalment is R = S × r / (1 − (1+r)^(−n)), where r = annual rate / 12 / 100 and n = remaining months. Total interest = R × n − S. Saving = original total interest − new total interest.
Example: PLN 10,000 overpayment on a PLN 300,000 mortgage
Mortgage: PLN 300,000 at 8% p.a., 240 months remaining. One-off overpayment: PLN 10,000. Shorten-term mode: saves approx. PLN 27,500 in interest, loan paid off ~14 months earlier. Reduce-instalment mode: monthly instalment drops by ~PLN 91, interest saving ~PLN 21,800.
Frequently asked questions
Results are indicative only and do not constitute financial or legal advice. Actual savings depend on your bank's schedule, the exact date of overpayment and any applicable early-repayment fees. Always check your loan agreement before making an overpayment.
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