Calculate∑ What your result means
Overpaying a repayment mortgage reduces the balance interest is charged on straight away, which both shortens the loan term and cuts the total interest paid over its life.
Mortgage Overpayment Calculator
See how much interest and time you could save by overpaying your mortgage each month.
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Verified for 2026-27Methodology 2026-27.1 · reviewed 2026-08-08 · review by 2027-03-01
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Payment timeline
Amortization schedule
Updates instantly when you change an input.
| Year | Principal repaid | Interest paid | Total paid |
|---|---|---|---|
| 1 | £8,112 | £10,798 | £18,909 |
| 2 | £16,681 | £21,138 | £37,819 |
| 3 | £25,734 | £30,994 | £56,728 |
| 4 | £35,297 | £40,340 | £75,637 |
| 5 | £45,400 | £49,147 | £94,546 |
| 6 | £56,073 | £57,383 | £113,456 |
| 7 | £67,347 | £65,018 | £132,365 |
| 8 | £79,258 | £72,016 | £151,274 |
| 9 | £91,840 | £78,343 | £170,184 |
| 10 | £105,133 | £83,960 | £189,093 |
| 11 | £119,175 | £88,827 | £208,002 |
| 12 | £134,009 | £92,903 | £226,912 |
| 13 | £149,680 | £96,141 | £245,821 |
| 14 | £166,235 | £98,495 | £264,730 |
| 15 | £183,723 | £99,916 | £283,639 |
| 16 | £200,000 | £100,353 | £300,353 |
Compare scenarios
Change remaining term to see the effect on your result.
Understand your result
Clear context for the values above.
Remaining balance
Remaining balance is included so you can interpret this estimate and make a better-informed comparison.
Interest rate
Interest rate is included so you can interpret this estimate and make a better-informed comparison.
Remaining term
Remaining term is included so you can interpret this estimate and make a better-informed comparison.
Extra monthly overpayment
Extra monthly overpayment is included so you can interpret this estimate and make a better-informed comparison.
How to use this calculator
- 1Enter your current remaining balance, interest rate, remaining term, extra monthly overpayment, annual penalty-free overpayment allowance, early repayment charge on excess.
- 2Review the headline estimated interest saved and the supporting figures beside it.
- 3Change one input at a time to see which assumption has the biggest effect.
- 4Confirm current UK rates and thresholds with an official source before acting.
Explore this calculator
What your result means →The headline estimated interest saved is based on the inputs currently shown above.Key terms explained →Review the assumptions, applicable rules, timing and real-world fees before making a decision.How to use this calculator →Enter your figures, review the live result, compare scenarios, then save or print your estimate.The calculation formula →The calculation follows the standard relationship between the displayed inputs. Results update whenever an input changes.Worked example →Using the current values produces £29,833.Assumptions and limitations →Review the assumptions, applicable rules, timing and real-world fees before making a decision.Costs or factors not included →Review the assumptions, applicable rules, timing and real-world fees before making a decision.Frequently asked questions →How accurate is this estimate? What should I check before relying on it? Can I save or share the result?
▦ How this calculator works
The calculator simulates the mortgage month by month at the standard scheduled payment plus your overpayment, tracking when the balance reaches zero, and compares the total interest paid against the same simulation without any overpayment.
◇ Assumptions and what's not included
Many UK lenders cap penalty-free overpayments at around 10% of the outstanding balance per year on fixed-rate deals, and some products charge an Early Repayment Charge above that limit — this isn't checked here.
▤ What to do next
Check your mortgage terms for any overpayment limit or exit charges before committing to a regular overpayment amount, and confirm with your lender whether overpayments reduce your term or your monthly payment by default.
UK-specific contextFigures use GBP and current published rates and thresholds.
Reviewed for clarityUpdated 3 August 2026.
ImportantFor planning and educational use — not tax, legal or financial advice.
Your privacy mattersInputs stay in your browser.
Frequently asked questions
Is there a limit on how much I can overpay?+
Many lenders allow up to 10% of the outstanding balance per year without a penalty on fixed-rate deals — check your specific mortgage terms, as limits vary.
Does overpaying reduce my monthly payment or my term?+
It depends on your lender's default setting — some reduce the term while keeping payments the same (as modelled here), others recalculate a lower monthly payment instead.
Is overpaying always the best use of spare cash?+
Not necessarily — compare your mortgage rate against what you could earn in a savings account or pension with tax relief before deciding, especially if you have higher-interest debt elsewhere.
Does this work for interest-only mortgages?+
No, this assumes a standard repayment mortgage where each payment reduces the balance — interest-only mortgages behave differently.
Official references
Rules and thresholds used by this calculator are labelled for 2026–27 or formula-labelled period. Review the primary guidance before making a filing, borrowing, benefit or investment decision.
Last source review: 3 August 2026. Calculator results are estimates and may exclude circumstances described in the methodology.