What is OverpaymentCalc?
OverpaymentCalc is a free, independent online calculator that shows UK homeowners exactly how much money and time they can save by making overpayments on their repayment mortgage. We built it because most people have no idea just how dramatically even a modest monthly overpayment can change their financial future.
On a typical £200,000 mortgage at 4.5% with 25 years remaining, overpaying just £200 per month saves over £30,000 in interest and cuts six years from the term. That's the kind of number that changes decisions — and it's what OverpaymentCalc is designed to show you clearly.
How the calculator works
The calculator uses standard mortgage amortisation mathematics to model your repayment mortgage month by month. It applies your overpayment — whether monthly, a lump sum, or both — directly to the outstanding capital balance each month, then recalculates the interest charged on the reduced balance. The cumulative difference in interest paid is your saving.
We show a year-by-year breakdown of your balance with and without overpayments, so you can see exactly how quickly your mortgage shrinks under each scenario.
Who built this?
OverpaymentCalc is an independent public resource. We are not a mortgage broker, lender, or financial adviser. We do not earn referral fees or commissions from any financial product. The site is funded entirely by advertising displayed on the page.
Is this financial advice?
No. OverpaymentCalc is a calculation and information tool only. Results assume a fixed interest rate for the full remaining term, which may not reflect your actual mortgage. We strongly recommend checking your mortgage terms for Early Repayment Charges before overpaying, and speaking to a qualified mortgage adviser if you are unsure.
Ready to calculate? Head back to the calculator to see how much you could save. It takes under 2 minutes.