Mortgage Overpayment Calculator
See how much time and interest you save by overpaying your mortgage. Compare overpayment vs investing.
Interest saved
£6,923
Overpayment
Check your mortgage terms — most fixed-rate deals charge 1–5% ERC (Early Repayment Charge) if you overpay more than 10% of the balance per year.
Enter your expected return after tax. Returns in an ISA are tax-free.
How is investment growth taxed?
| Wrapper | Tax on growth |
|---|---|
| ISA | None — tax-free (£20k/yr allowance) |
| General account | CGT: 18–24% on gains above £3k allowance |
| Savings account | Income tax after £1k (basic) / £500 (higher) allowance |
| Pension (SIPP) | Tax-free inside; taxed as income on withdrawal |
Interest saved
£6,923
Time saved
1 yr 2 mo
New payoff
December 2044
February 2046
Month 1 saving
£0
Year 1 saving
£13
Your mortgage debt over time
Compared to saving at 7%
£23,339
Savings pot
£17,226
Still owed
£6,113 left over after clearing mortgage
You'd be £6,113 better off saving at 7% rather than overpaying for the 18 years and 10 months it'd take. If you saved instead, you'd have £23,339 in savings but still owe £17,226 on the mortgage — more than enough to clear it with £6,113 left over. However, investment returns are not guaranteed.
See how much you could borrow →
Reassessing your mortgage? Check your borrowing power based on income
Early Repayment Charges (ERC)
Most fixed-rate mortgages charge 1–5% of the amount overpaid if you exceed the annual overpayment allowance — typically 10% of the outstanding balance per year. Check your mortgage terms before making large overpayments. ERCs usually don't apply to tracker or standard variable rate mortgages.
Investment returns are not guaranteed and can go down as well as up. Mortgage interest savings are guaranteed if your rate is fixed.