Free mortgage overpayment calculator
Estimate interest savings, time saved, and your balance over time when you add a regular monthly overpayment.
No account needed
Runs in your browser
Built for quick comparisons
Example scenario
£38,458
Estimated interest saved with a £200 monthly overpayment on the default mortgage.
Inputs
Private
Runs in browser
Estimate
Estimated interest saved
£38,458
Estimated time saved
5 years 1 months
Current payment
£1,390
New payoff term
19y 11m
Assumes the rate stays the same and every overpayment reduces the balance immediately.
Projection
This calculator provides estimates only and does not constitute financial advice. Mortgage calculations may vary depending on lender terms, overpayment limits, interest rate changes, fees, and repayment structures. Always consult a qualified financial advisor or your mortgage provider before making financial decisions.
Calculator guide
Use the calculator to compare your current repayment path with a regular monthly overpayment. The most useful inputs are your current outstanding balance, the interest rate you want to model, the years left on the mortgage, and the extra amount you could comfortably pay each month.
The result is an estimate, not a lender statement. It is best used for comparing scenarios: for example, whether an extra payment of 50, 100, or 250 a month could make a meaningful difference before you commit real cash.
Step 1
Enter the outstanding balance, interest rate, and years left. The calculator estimates the standard monthly repayment for that remaining term.
Step 2
The overpayment is applied alongside the estimated standard repayment, reducing the balance sooner than the base schedule.
Step 3
The result compares the base repayment path with the overpayment path, showing estimated interest saved and how much earlier the balance could reach zero.
Check whether your mortgage has an overpayment allowance, early repayment charge, or a specific process for choosing whether overpayments reduce the term or the required monthly payment.
It is also worth comparing overpayments with other uses of cash, such as emergency savings, high-interest debt repayment, pension contributions, or investing.
Common questions
Earlier payments usually reduce the balance sooner, which can reduce future interest. A lump sum can be powerful if you have spare cash, while monthly overpayments may be easier to budget. The best choice depends on your lender rules, emergency savings, and other debts.
They can. Some mortgage deals allow overpayments up to a set limit, while payments above that limit may trigger an early repayment charge. Always check your mortgage offer or ask your lender before making large overpayments.
Not always. Mortgage overpayments can offer a clear interest saving, but you may want emergency savings first and may prefer to repay higher-interest debts before overpaying a mortgage. Investing adds risk and may perform better or worse than the mortgage interest saved.
It depends on how your lender applies overpayments. Some borrowers choose to keep the monthly payment similar and shorten the term; others reduce the required monthly payment. Check your lender's process before assuming which outcome will apply.
Keep learning
Understand allowances, early repayment charges, and lender restrictions.
Read guide →
See why payment size, interest rate, and timing affect potential savings.
Read guide →
Compare certainty, risk, liquidity, and long-term return potential.
Read guide →
Compare monthly, annual, and occasional overpayment patterns.
Read guide →
Before making a real overpayment, compare the estimate with your lender's terms and independent guidance.
Tune your overpayment
Jump back to the calculator.