FREE MORTGAGE TOOL
Mortgage Overpayment Calculator
See how much interest you could save and how much earlier you could be mortgage-free by overpaying your mortgage. Enter your remaining balance, term and rate, then add the extra amount you could pay each month or as a one-off lump sum.
Illustrative only — not advice
No sign-up needed
WORKED EXAMPLE
What £100 a month could do
On a £150,000 mortgage at 4.5% with 25 years left, paying £100 a month extra could mean:
Normal payment: £834 a month. Illustrative only, using the assumptions below.
Try your own figuresWork out your overpayment
Enter your figures below. The calculator updates as you type.
The results are illustrative only and are not advice. They assume your rate stays the same for the whole term and that overpayments are applied exactly as you enter them. In practice, criteria and deals vary, and your lender’s terms decide what is possible — always check your mortgage terms or get a specific quote from your lender before acting on any figure here.
This calculator needs JavaScript to show results. The figures it produces are always illustrative only and are not advice — see the assumptions listed below the calculator.
Year-by-year balance
| Year | Balance without overpayments | Balance with overpayments |
|---|
Illustrative only — not advice. See the assumptions below the calculator.
Many deals limit penalty-free overpayments to 10% of the outstanding balance a year, and paying more than your allowance could trigger an Early Repayment Charge. Your home may be repossessed if you do not keep up repayments on your mortgage.
If you are unsure what your deal allows, get in touch with our team and we’ll talk it through.
Assumptions behind the calculator
The calculator is a ready reckoner. Results rely on these assumptions:
- Your interest rate stays the same for the whole remaining term. In reality, rates change when a deal ends, and a new deal may have a different rate.
- Overpayments are applied exactly as entered, with no charge, and your lender accepts them in full.
- The calculation keeps your payment the same and shortens the term. Some lenders instead reduce the monthly payment, and some offer both options — check which applies to yours.
- No fees, insurance, tax or rate changes are modelled.
- Results are rounded and for illustration only; they are not a quote, a prediction or advice. Always get a specific quote from your lender before making decisions.
Page last reviewed: November 2026. This tool is for illustration only and is not advice.
HOW IT WORKS
How overpayments work
Overpaying means paying more than your required monthly payment, either regularly or as a one-off lump sum. Because interest is charged on your outstanding balance, a smaller balance means less interest, and the effect compounds over the years that remain.
Many deals let you overpay up to 10% of your balance each year without a charge, but it varies between lenders and products, so check your own terms first.
01
EVERY MONTH
Regular monthly overpayments
Even £50 or £100 extra a month can shorten your term and reduce the interest you pay, depending on your balance and rate.
- A fixed amount on top of your payment
- Builds up steadily over time
- Check your lender’s yearly allowance
02
ONE-OFF
Lump sums
A bonus, inheritance or savings can be applied as a one-off reduction to your balance.
- Reduces your balance in one go
- Keep enough savings for emergencies
- Watch for Early Repayment Charges
On a £150,000 balance, 25 years remaining and a 4.5% rate, the monthly payment would be about £833. Adding £100 a month could shorten the term by roughly three years and save several thousand pounds in interest, depending on the exact figures. These are round-figure illustrations of the maths, not a quote or a prediction — the calculator above works on your own numbers.
Your overpayment allowance
Many deals allow 10% of the outstanding balance a year penalty-free, but the allowance varies by deal, and some allow more.
Early Repayment Charges
Paying above your allowance could trigger a charge; the terms are in your mortgage offer documents.
Your emergency fund
Overpayments are hard to get back, so accessible savings usually come first.
More expensive debts
Credit cards and loans usually charge more than a mortgage, so clearing them first often makes sense.
Your rate
The lower your rate, the smaller the interest saving from overpaying.
If you want to read more, our guide to reviewing your mortgage before your deal ends explains how to weigh an overpayment against a product change, and our remortgage advice page covers switching deals when your current one ends.
WORTH KNOWING
When overpaying may not be the best use of money
Overpaying is not automatically the right call. Money paid into your mortgage is effectively locked into your home — getting it back generally means remortgaging or a further advance, subject to lender agreement. It can make sense to keep accessible savings for emergencies first, to clear more expensive debt first, or to take advice before committing a large lump sum. The right answer depends on your circumstances.
If your deal is ending soon, compare whether overpaying, a product transfer or a remortgage does more for you: our guide on product transfer or remortgage sets out the trade-offs.
Not sure what’s right for you?
An adviser can look at your deal, your savings and any other borrowing with you, then explain your options.
MORTGAGE OVERPAYMENT FAQs
Questions About Overpaying Your Mortgage
Thinking about making mortgage overpayments? Your lender’s terms define the limits and charges, while your wider plans matter too. Check your offer before acting.
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Book Your Initial ConversationCan I overpay my mortgage every month?
What is an Early Repayment Charge?
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How much could I save by overpaying £100 a month?
Can I get overpayments back if I need the money?
Should I overpay or clear other debts first?
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