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Mortgage Overpayment Calculator

See the dramatic effect of even small monthly overpayments on your mortgage term and total interest.

Short answer

Overpaying just £100/month on a typical UK mortgage shaves 2–3 years off the term and saves £10,000+ in interest. Most lenders allow up to 10%/yr penalty-free.

Your mortgage

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yrs
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Calculation method, coverage and version

Inputs used
Outstanding balance, Interest rate, Years remaining, Extra monthly payment.
Calculation approach
The calculator applies the rules and assumptions described in “How it works” to the values you enter. Rounding can cause small differences from an official or provider calculation.
Coverage
Mortgages & Money. UK nations, tax treatment, local rules and provider criteria can differ; check the official sources shown below before acting.
Content version
No page-specific review date is currently published. Treat the result as indicative and verify current rules independently.
Not included unless explicitly requested: personal circumstances not entered, provider discretion, future rule changes, professional fees and case-specific exceptions. Read the full calculator methodology.

Primary sources and official verification

Use these official sources to verify current rules before acting. Coverage and dates can differ across England, Scotland, Wales and Northern Ireland.

See the sitewide source policy.

How it works

Each extra £ goes 100% to principal, reducing future interest charges. The earlier you overpay, the more interest you avoid — overpayments in year 1 save much more than the same amount in year 20.

Worked example

£180k at 4.5% over 22 years: £1,074/mo, £103,544 total interest. Adding £150/mo extra: clears in 17.6 years, saves ~£28,000 interest.

Who should use this

  • •Anyone with spare cashflow each month
  • •Borrowers near the end of a fix who want to reduce balance before remortgaging
  • •Pre-retirees clearing the mortgage

Common mistakes

  • ×Overpaying past the lender's allowance and triggering ERCs (typically 1–5%)
  • ×Overpaying when high-interest debt (credit cards) still exists
  • ×Forgetting an emergency fund — overpayments are hard to get back

Frequently asked questions

Should I overpay or invest?▾

Mathematically: invest if expected returns > mortgage rate after tax. Emotionally: many prefer the certainty of a smaller mortgage.

Reduce term or reduce monthly?▾

Reducing the term saves more interest. Reducing monthly gives flexibility but lets the loan run full term unless you keep overpaying.

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