Why overpaying works
Every pound you overpay goes straight to reducing the capital. From the next month on, you pay interest on a smaller balance. Your normal monthly payment stays the same, so more of each future payment also goes to capital. The effect compounds over the whole term. That’s why small regular overpayments early on make a big difference.
Worked example: £200,000 at 4.5% over 25 years
| Overpayment | Interest saved | Mortgage-free sooner by |
|---|---|---|
| £100 a month | £21,142 | 3 yrs 6 mo |
| £250 a month | £42,366 | 7 yrs 2 mo |
| £2,000 once a year | £30,433 | 5 yrs 1 mo |
Without overpaying, total interest would be £133,501. The calculator shows a return on £1 figure: how much interest each pound of overpayment saves over the life of the loan.
Reduce the term or reduce the payment?
When you overpay, most lenders let you choose:
- Reduce the term. Your payment stays the same and you finish sooner. This saves the most interest.
- Reduce the payment. You keep the same end date, but your monthly payment is recalculated lower. This is useful if you want breathing room, for example before a baby or a career break.
Switch between them under Use overpayments to and compare the results.
Early repayment charges (ERCs)
During a fixed or discounted deal, most lenders cap penalty-free overpayments, typically at 10% of the balance per year. Go over the limit and an early repayment charge of 1–5% applies to the excess. The calculator checks every year of your plan against the limit you set and warns you about the first month you’d go over.
Once your deal ends and you’re on the lender’s standard variable rate, there’s usually no limit. You’d also normally remortgage at that point. Many people time big lump sums to just before a remortgage so they move to a lower loan-to-value band and get a cheaper rate.
Overpay or save?
Overpaying gives a guaranteed, tax-free return equal to your mortgage rate. Before you overpay, check:
- Do you have an emergency fund? Money paid into a mortgage is hard to get back out.
- Do you have more expensive debt? Credit cards at 20%+ should go first. Use the debt payoff planner.
- Can you beat your mortgage rate tax-free? Compare with a cash ISA in the savings calculator.
- Are you getting the full employer pension match? Free money beats almost anything.
An offset mortgage is another option. Your savings reduce the interest you pay but stay available.
How the calculation works
We build the full month-by-month schedule twice, with and without overpayments, using monthly interest at your rate. Regular overpayments are applied every month. The yearly amount is applied in month 12 of each year. A one-off lump sum is applied in the month you choose. The final payment is adjusted so the balance ends at exactly £0.
Frequently asked questions
How much does overpaying £100 a month save?
On a £200,000 mortgage at 4.5% over 25 years, an extra £100 a month saves about £21,142 in interest and clears the mortgage 3 years and 6 months early.
Is it better to overpay monthly or as a lump sum?
The earlier money goes in, the more it saves. A £10,000 lump sum in the first month of that same mortgage saves about £19,197 and cuts 26 months. Regular monthly overpayments are easier to sustain and stay inside most penalty-free limits.
How much can I overpay without a penalty?
Most fixed and tracker deals let you overpay up to 10% of the balance each year without an early repayment charge. Some allow less, and some lenders count the limit from the deal start date. Check your mortgage offer.
Should I reduce my term or my monthly payment?
Reducing the term saves the most interest. Reducing the payment keeps the same end date but lowers your monthly outgoings, which gives you flexibility. Our calculator models both.
Should I overpay or save?
Overpaying earns you your mortgage rate, risk-free and tax-free. If you can earn more than that in a tax-free savings account after keeping an emergency fund, saving may come out ahead — and keeps your money accessible.
Do overpayments reduce my monthly payment automatically?
It depends on the lender. Many reduce the term by default. Some recalculate the payment, often once a year.
Are overpayments better early or late in a mortgage?
Early. More of each payment goes to interest in the early years, so overpaying then saves the most.
Sources
Results are estimates for education and planning, not financial advice. They depend on the figures you enter and the assumptions shown above.