Mortgage Overpayment Calculator — Term & Interest Saved

See how monthly mortgage overpayments shorten your term and cut total interest (UK-style term reduction).

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Formula

Standard amortized payment M = B·r·(1+r)^n / ((1+r)^n − 1); with overpayment the payment becomes M + X and the balance is simulated month by month until it reaches zero — the term shortens instead of the payment dropping.

Examples

InputResult
£150,000 at 4.5%, 20 yrs left, +£100/mo206 months instead of 240 (2.8 years earlier) · £12,413 interest saved
£200,000 at 5%, 25 yrs left, +£200/mo226 months instead of 300 (6.2 years earlier) · £41,843 interest saved
£100,000 at 3%, 15 yrs left, +£50/mo165 months instead of 180 (1.3 years earlier) · £2,151 interest saved

Frequently Asked Questions

What is a mortgage overpayment?

Paying more than your required monthly repayment, with the extra going straight to the principal. On most UK mortgages this reduces the term and total interest rather than the monthly payment.

How is overpaying different from recasting?

In the UK, overpaying typically keeps your monthly payment the same and shortens the term — that is what this calculator shows. Recasting (more common in the US) re-amortizes to lower the payment while keeping the term.

Will my lender charge me for overpaying?

Many UK deals allow 10% of the balance per year penalty-free; beyond that an early repayment charge (ERC) may apply — typically 1–5%. Check your offer document before overpaying.

Is overpaying better than saving the money?

If your mortgage rate is higher than the after-tax return on savings, overpaying wins mathematically — but keep an emergency fund first, since equity in a home is hard to get back out.

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Disclaimer: This calculator is for informational and educational purposes only and does not constitute financial, investment, tax or legal advice. Results are estimates — actual returns, rates and terms vary. Consult a qualified financial professional before making financial decisions.