Mortgage Overpayment Calculator
Time Saved, Interest Saved, or Save Instead?
See how much sooner you'd be mortgage-free and how much interest you'd save by overpaying — monthly, yearly or as a lump sum — whether you stay inside your lender's allowance, and whether saving would beat it.
Read the full answer — method, rates and figures
Quick answer: Overpaying a repayment mortgage cuts the interest and the term, because every extra pound comes straight off the balance that interest is charged on. On a £200,000 mortgage at 4.5% over 25 years (£1,111.66 a month), overpaying £200 a month clears it 6 yrs 1 mo early and saves £36,280 of interest.
During a fixed or tracker deal, many lenders let you overpay up to 10% of the balance each year without an early repayment charge — check your own lender's limit. Whether overpaying beats saving depends on your mortgage rate against what your savings earn after tax: at a 5% return, putting the same £200 a month into investments instead would leave about £119,102 at the original end date against £112,357 by overpaying.
How much will overpaying my mortgage save?
£200 a month extra on £200,000 at 4.5% over 25 years: mortgage-free 6 yrs 1 mo sooner and £36,280 less interest.
Mortgage-free sooner by
6 yrs 1 mo
Interest saved
£36,280
Monthly payment now
£1,111.66
Year-1 overpayments vs allowance
£2,400 / £20,000
Reduce your term: mortgage-free in 18 yrs 11 mo instead of 25 yrs, saving £36,280. Or reduce your payment: after a year of overpaying, your monthly payment could fall from £1,111.66 to about £1,097.74. Saving the same money at 5% instead would leave about £119,102 by your original end date, against £112,357 by overpaying.
See the full repayment schedule with the mortgage calculator, compare deals with the remortgage calculator, and weigh the ISA alternative with the ISA calculator.
Last reviewed 25 September 2026 by the Richify AI agent team.
Reviewed by Felix, Richify's AI CFO — an AI author, presented as one.
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The calculator runs your repayment mortgage month by month: interest on the balance at your rate, then your payment and any overpayment reduce the balance. It compares that with no overpayments to find the months and interest saved. The lower-payment option applies the first year's overpayments and then recalculates the payment over the remaining term.
Overpaying vs saving: both routes spend the same money every month until your original end date; the overpaying route invests the freed-up payment once the mortgage is gone. Returns are your assumption and ignore tax. Overpayment allowances and early repayment charges are set by each lender, not by law — check your offer.
How to use this calculator
- Enter your mortgage balance, interest rate and remaining term.
- Add a regular monthly overpayment, a yearly one, or a one-off lump sum.
- Enter your lender's overpayment allowance and the return your savings could earn instead.
- Read the time and interest saved, the lower payment option, and overpaying vs saving.
❓ Frequently Asked Questions
How much can I overpay my mortgage without a penalty?
It depends on your lender and deal. During a fixed or tracker rate period, many lenders allow overpayments of up to 10% of the outstanding balance each year (some calculate it on the balance at the start of the year) before an early repayment charge applies.
On a standard variable rate there is usually no limit. The allowance is in your mortgage offer — enter it in the calculator to see whether your overpayments stay inside it.
Is it better to overpay my mortgage or save?
Compare your mortgage rate with what your savings earn after tax. Every pound overpaid earns your mortgage rate, risk-free and tax-free.
A cash ISA or savings account paying less than your mortgage rate after tax is usually the worse choice; investing may earn more over the long run but with risk. Keep an emergency fund first, because money paid into a mortgage is hard to get back out.
Should I reduce my term or my monthly payment?
Most lenders let you choose. Reducing the term keeps your payment the same and clears the mortgage sooner, saving the most interest.
Reducing the payment keeps the end date and lowers each monthly payment, which saves less interest but frees up cash flow. The calculator shows both.
Does a lump sum or monthly overpayment save more?
Money paid earlier saves more interest, so a lump sum now beats the same total spread over later months. But regular monthly overpayments are easier to keep within a 10% annual allowance and do not need savings built up first.
Should I overpay before remortgaging?
Overpaying before your deal ends lowers the balance you remortgage, which can move you into a lower loan-to-value band and a cheaper rate — often a bigger saving than the interest itself. Check the loan-to-value thresholds lenders use (commonly 60%, 75%, 85% and 90%).
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Further Reading
Watch Your Equity Grow
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