Mortgage Overpayment Calculator
Enter your current mortgage details and a monthly overpayment to see how much interest you save and how many years you shave off your term.
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Results are estimates only. Actual savings depend on your lender's terms and whether overpayments reduce the term or the monthly payment.
Overpayment examples — £200,000 balance at 4.5%
Monthly payment of £1,050. Click any row to load it into the calculator above.
| Monthly overpayment | Interest saved | Time saved | New term |
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How overpayments work
When you make an overpayment, the extra amount goes directly towards reducing your outstanding balance. Because your balance falls faster, less interest accrues each month — which means more of your standard payment also goes towards capital. The effect compounds over time.
Most lenders give you a choice: reduce your monthly payment (keeping the same term) or keep the same monthly payment (shortening the term). Keeping the same payment is almost always better financially as it maximises interest saved.
This calculator assumes overpayments shorten the term while keeping your standard monthly payment the same.
Frequently asked questions
Most lenders allow penalty-free overpayments of up to 10% of the outstanding balance per year during a fixed-rate period. On a tracker or standard variable rate mortgage there is typically no limit. Check your mortgage offer document.
If your mortgage interest rate is higher than the after-tax return on savings, overpaying is usually better. With current high savings rates you should compare carefully — a Cash ISA or high-interest savings account could beat the benefit of overpayment.
Some mortgages have an "overpayment reserve" that lets you borrow back overpayments you've made. This is sometimes called a flexible mortgage or offset feature. Check with your lender — it's not available on all products.
Most lenders allow penalty-free overpayments of up to 10% of the outstanding balance per year. Check your mortgage terms before making large overpayments — early repayment charges may apply if you exceed this.