Use this mortgage overpayment calculator to see how much interest you save, and how much sooner you are mortgage-free, by paying more than your normal monthly payment. Add a regular monthly overpayment, a one-off lump sum, or both.
What overpaying saves you
- Interest saved
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- Time saved
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- Mortgage-free in
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- Normal monthly payment
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| Without overpaying | With overpayments |
|---|
Assumes your rate stays the same for the rest of the term and overpayments reduce your term, not your monthly payment.
In the example, a £200,000 mortgage at 4.5% over 25 years costs £1,111.66 a month. Overpaying £200 a month saves £36,280 in interest and clears the mortgage 6 years 1 month early.
How to use the mortgage overpayment calculator
- Enter your mortgage balance. Use the amount you still owe, not the amount you first borrowed. It is on your annual mortgage statement or online account.
- Enter your interest rate and the number of years left on your mortgage.
- Add a monthly overpayment, a lump sum, or both.
- Read your results. The table compares your mortgage with and without overpayments.
How the mortgage overpayment calculator works out your saving
Mortgage interest is charged on the balance you owe. Every pound you overpay comes straight off that balance, so from the next month you pay interest on a smaller amount. Because your normal payment stays the same, more of each payment goes towards the balance, and the mortgage ends sooner.
The earlier you overpay, the more you save, because that money stops attracting interest for longer. A £10,000 lump sum in the first year of a 25-year mortgage saves far more than the same amount paid in year 20.
Monthly overpayment examples
This table shows what the mortgage overpayment calculator gives for different monthly overpayments to a £200,000 repayment mortgage at 4.5% over 25 years:
| Extra each month | Mortgage-free in | Time saved | Interest saved |
|---|---|---|---|
| £50 | 23 years 2 months | 1 year 10 months | £11,534 |
| £100 | 21 years 6 months | 3 years 6 months | £21,142 |
| £200 | 18 years 11 months | 6 years 1 month | £36,280 |
| £300 | 16 years 11 months | 8 years 1 month | £47,708 |
| £500 | 14 years | 11 years | £63,887 |
Lump sum overpayment examples
Use the lump sum box in the overpayment mortgage calculator for a one-off payment, for example from a bonus, an inheritance or savings, also cuts your interest. Here is the effect of a lump sum paid today on the same mortgage:
| Lump sum now | Time saved | Interest saved |
|---|---|---|
| £5,000 | 1 year 1 month | £10,011 |
| £10,000 | 2 years 2 months | £19,300 |
| £20,000 | 4 years 2 months | £35,968 |
How your interest rate changes the saving
The higher your rate, the more each overpayment saves. Here is the effect of overpaying £200 a month on a £200,000, 25-year mortgage at different rates, worked out with the same mortgage overpayment calculator method:
| Interest rate | Normal payment | Time saved | Interest saved |
|---|---|---|---|
| 3.5% | £1,001.25 | 5 years 11 months | £26,187 |
| 4.5% | £1,111.66 | 6 years 1 month | £36,280 |
| 5.5% | £1,228.17 | 6 years 3 months | £47,770 |
| 6.5% | £1,350.41 | 6 years 5 months | £60,783 |
If your rate rises when your deal ends, overpaying becomes more valuable. If you are on a very low fixed rate, saving the money and overpaying later can make sense.
How to make an overpayment
- Check your mortgage offer or online account for the overpayment allowance and any early repayment charge.
- Decide how you want it applied: to shorten the term or to lower your monthly payment.
- Pay through your lender’s app, by bank transfer or by phone. For regular overpayments, many lenders let you raise your Direct Debit.
- Keep a record and check your next statement to make sure the balance has dropped.
Track your own allowance: lenders usually count the 10% from your balance on a set date each year, and unused allowance does not carry over.
Shorter term or lower payments?
When you overpay, many lenders let you choose between two options:
- Reduce your term: your monthly payment stays the same and the mortgage ends sooner. This saves the most interest, and it is what this overpayment mortgage calculator shows.
- Reduce your monthly payment: your term stays the same and future payments drop. You save less interest, but your budget gets more breathing room.
Some lenders reduce the payment automatically after a lump sum. If you want to keep the term shorter, tell your lender or keep paying the old amount as a regular overpayment.
Overpayment limits and early repayment charges
During a fixed or discounted deal, many lenders let you overpay up to 10% of your balance a year without a fee. Above that, you may pay an early repayment charge, often 1% to 5% of the amount over the limit. The mortgage overpayment calculator warns you if your overpayments in the first year go above 10%.
Once your deal ends and you move to the lender’s standard variable rate, there is usually no limit. Always check your mortgage offer or ask your lender before making a large overpayment.
Should you overpay your mortgage?
An overpaying mortgage calculator shows the saving, but overpaying is not right for everyone. It is a guaranteed return equal to your mortgage rate, but not always the best use of spare money. Before you overpay, check these first:
- Pay off dearer debts first. Credit cards and personal loans usually cost more than your mortgage.
- Keep an emergency fund. Money paid into your mortgage is hard to get back. Keep at least three months of living costs in easy-access savings.
- Compare savings rates. If a savings account pays more after tax than your mortgage rate, saving may beat overpaying.
- Think about your pension. Pension contributions get tax relief and often extra money from your employer.
If you want flexibility, an offset mortgage uses your savings to reduce the interest without locking the money away. Our offset mortgage calculator compares the two.
Overpaying when you remortgage
The end of a fixed deal is a good time to make a large overpayment, because early repayment charges no longer apply. Paying down your balance can also move you into a lower loan-to-value band and a cheaper rate. Use our remortgage calculator to compare new deals.
Mortgage overpayment calculator UK: worked example
Aisha owes £200,000 at 4.5% with 25 years left. She pays a £5,000 bonus off now and adds £150 a month. The mortgage overpayment calculator shows she will be mortgage-free in 19 years 4 months and save £36,415 in interest. Her first-year overpayments are £6,800, which is under 10% of her balance, so no charge applies on most deals.
Related mortgage calculators
See how much interest your mortgage costs year by year with the mortgage interest calculator, or compare paying only the interest with the interest only mortgage calculator. Thinking of letting a property? Try the buy to let mortgage calculator.
Frequently asked questions
Is it better to overpay monthly or in a lump sum?
Pound for pound, the sooner the money is paid, the more it saves, so a lump sum today beats the same total spread over several years. Monthly overpayments are easier for most budgets, and you can combine both.
Does overpaying reduce my monthly payment?
Not usually. Most lenders keep your payment the same and shorten the term, unless you ask them to recalculate it. Check with your lender which they do.
Can I get overpayments back?
Only on some flexible mortgages that allow payment holidays or “borrow back”. On most mortgages, overpaid money cannot be withdrawn.
How accurate is this early mortgage repayment calculator?
It uses the standard monthly interest formula lenders use. Real figures can differ slightly because lenders calculate interest daily or apply overpayments on different dates, and your rate will change when your deal ends.
Will overpaying improve my credit score?
Not directly. It lowers your debt over time, which can help future borrowing, but credit scores mainly reflect paying on time.
About this calculator
This mortgage overpayment calculator works out your mortgage month by month using the standard repayment formula, then applies your overpayments. It assumes your interest rate stays the same and that overpayments reduce your term. Guidance on overpaying was checked against MoneyHelper on 5 November 2026.
Results are estimates for planning. Your lender can give exact figures and confirm any charges.