How much does overpaying your mortgage actually save?
Enter your mortgage details and overpayment amount. See the exact interest saved, years knocked off, and a chart showing your balance shrink faster than you thought possible.
7 min readUpdated 16 Aug 2026UK
Your mortgage
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%
yrs
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Leave as calculated or enter your actual payment
Regular monthly
One-off lump sum
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Extra paid every month on top of your normal payment
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A single payment — e.g. a bonus, inheritance or savings pot
mo from now
0 = today. The earlier you pay, the more interest you save.
Results
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Enter your mortgage details to see how much overpaying saves you.
Enter your balance, rate, remaining term and current payment, then add a monthly overpayment or lump sum to see the interest saved and years cut off your mortgage.
Mortgage balance over time
Normal repayment vs with overpayments
Normal
With overpayments
Key takeaways
Overpaying saves interest for the whole term. Every pound off the balance stops interest on that pound every remaining month, so it compounds.
Earlier is better. A lump sum paid early saves far more than the same sum paid years later — there's more time for the saving to stack up.
It's a guaranteed, tax-free return. Overpaying earns you your mortgage rate with no risk — hard to beat with savings after tax.
Mind the 10% cap. Most fixed deals allow up to 10% of the balance a year before an early repayment charge; trackers usually have no limit.
Emergency fund first. Keep 3–6 months of expenses accessible before overpaying — and compare with investing instead.
Got a one-off sum — a bonus, an inheritance or the proceeds of a house sale — and wondering what happens if you pay it straight off your mortgage? Switch the calculator above to One-off lump sum mode, enter the amount and when you'd pay it, and you'll see two numbers instantly: the interest saved and the time knocked off your term.
How much could a one-off lump sum save you?
A lump sum works by cutting your outstanding balance in one go. Because interest is charged on that balance every month, a lower balance means less interest for every remaining month of the mortgage — so a single payment keeps saving you money for years. The bigger the sum and the more term you have left, the larger the saving.
Worked example: £20,000 lump sum on a £220,000 mortgage
Take a £220,000 mortgage at 4.5% with 22 years to run. Paying a £20,000 lump sum today saves roughly £30,000 in interest and clears the mortgage around 3 years 2 months early — without changing your monthly payment. Wait five years to pay the same £20,000 and the saving drops noticeably, because the balance stays higher for longer. Enter your own figures above for an exact result.
Lump sum vs monthly overpayment — which saves more?
Pound for pound, a lump sum paid today beats the same total dripped in monthly, because the whole amount stops accruing interest immediately rather than in instalments. If you have the cash now and no early repayment charge applies, the lump sum is usually the more efficient route. A regular monthly overpayment wins on affordability — it's easier to commit £200 a month than to find £20,000 at once.
Are there overpayment limits or early repayment charges?
Most UK fixed-rate mortgages let you overpay up to 10% of the outstanding balance each year penalty-free — £22,000 on a £220,000 mortgage. Above that, an early repayment charge of typically 1–5% of the excess can apply. Tracker and variable deals usually have no limit. Always check your mortgage offer, or ask your lender, before sending a large lump sum.
When is the best time to make a lump sum overpayment?
As early as possible. A lump sum paid in year one avoids interest for the entire remaining term, while the same sum paid a decade later has far fewer years to work. If you're near the end of a fixed deal, it can also be worth timing the payment for when any early repayment charge no longer applies.
How do mortgage overpayments work in the UK?
Overpaying means paying more than your required amount — monthly or as a lump sum — to cut your outstanding balance. Most UK fixed-rate mortgages let you overpay up to 10% of the balance a year without early repayment charges (ERCs); tracker and variable mortgages usually have no restriction at all.
The benefit compounds: by reducing the principal, you cut the interest charged every subsequent month, so each overpayment saves interest for the rest of the term — and the earlier you pay, the longer that lower balance works for you.
In the calculator's default example — a £220,000 mortgage at 4.5% with a £200/month overpayment — you save around £42,800 in interest and become mortgage-free about 6 years 5 months early. That's a guaranteed, tax-free return equal to your mortgage rate on every pound overpaid, hard to match with savings after tax.
Before overpaying, keep an emergency fund of three to six months' essential expenses — money paid into your mortgage isn't easily retrievable — and clear any higher-rate debt first, since credit cards at 20–30% APR cost far more than a mortgage at 4–5%.
Why do even small overpayments save so much?
Because mortgage interest is charged on your outstanding balance, every pound you knock off stops interest on that pound for every remaining month. That's why overpaying early is so powerful — the saving compounds across decades, not just the month you pay.
Take the calculator's default: a £220,000 mortgage at 4.5% with a £1,180 monthly payment. Adding just £200 a month saves around £42,800 in interest and clears the mortgage roughly 6 years 5 months early — a guaranteed, tax-free return equal to 4.5% on every pound overpaid, better than most savings accounts after tax.
The 10% rule: Most UK fixed-rate mortgages allow overpayments of up to 10% of your outstanding balance per year without an early repayment charge (ERC). On a £220,000 mortgage, that's up to £22,000/year — far more than most people can realistically overpay. Check your mortgage terms before making large lump-sum payments.
Monthly overpayments or a lump sum — which is better?
Both save interest, but they suit different situations — regular overpayments build a habit, while a lump sum works hardest paid early. Regular monthly overpayments are ideal for people who can commit a fixed extra amount each month. They reduce the balance steadily, cutting interest every month, and build into a reliable habit. Most lenders make this easy via standing order.
Lump sum overpayments are most powerful when made early in the mortgage, because the capital reduction has longer to compound. A £5,000 lump sum made 10 years into a 25-year mortgage saves less interest than the same £5,000 made in year one — because in year one, that money avoids interest charges for 15 more years instead of 5. Use the calculator to compare the impact of your planned lump sum at different points in your term.
When does overpaying NOT make sense?
Overpaying isn't always the optimal move. You should prioritise other uses of money if:
You have no emergency fund. Aim for 3–6 months of essential expenses in accessible savings before overpaying. Mortgage money is illiquid — you can't retrieve it easily if circumstances change.
You have higher-rate debt. Credit card debt at 20–30% APR costs far more than a mortgage at 4–5%. Pay expensive debt first.
Your savings rate beats your mortgage rate. If a Cash ISA or savings account pays more than your mortgage rate (after tax), you're better off saving the money.
You're close to a fixed-rate deal end. Some lenders allow unlimited overpayments when you're close to remortgaging — or at least be aware of your ERC threshold.
How do you actually make an overpayment?
The most reliable method is a standing order paid into your mortgage alongside your normal direct debit, with lump sums sent by bank transfer. set up to pay into your mortgage alongside your normal direct debit. Pay on the same date as your regular payment, ensuring the extra lands on your mortgage account and is allocated to capital reduction. For lump sums, most lenders accept bank transfers directly to your mortgage account with a specific payment reference — call your lender first to confirm the reference needed and verify they'll treat it as capital repayment, not advance payment of future installments.
What is an offset mortgage, and is it better?
An offset mortgage links savings to your mortgage, so interest is charged only on the balance minus your savings — and you keep access to the money. Unlike overpaying, you retain access to the savings. If you're keeping a large emergency fund or saving for a specific goal, an offset mortgage can effectively "overpay" your mortgage while leaving your money accessible. The trade-off: offset rates are often 0.1–0.3% higher than standard mortgages, so the maths only works if your savings pot is substantial and you maintain it consistently.
How does overpaying help when you remortgage?
Overpayments reduce your balance and your loan-to-value, which can unlock a better rate at your next remortgage. When your fixed term ends, that lower LTV is an extra saving this calculator doesn't capture. A lower LTV typically means access to better interest rates when you remortgage — an indirect benefit of overpaying that this calculator doesn't capture. Reducing your LTV from 75% to 65% through a combination of time and overpayments can save 0.1–0.3% on your next mortgage deal, which on a large balance is significant on top of the direct interest savings shown here.
Common questions
Mortgage Overpayment FAQs
It depends on your remaining term, rate and balance, but as a rule of thumb, a lump sum paid early in the mortgage saves more than the same amount paid later, because it stops accruing interest sooner. A £20,000 lump sum on a £220,000 mortgage at 4.5% with 20 years left typically saves several thousand pounds and cuts months off the term — use the calculator above for your exact figures.
A lump sum paid today saves more interest than the same total paid gradually over a year, because the whole amount stops accruing interest immediately rather than in instalments. If you have the cash available now and no early repayment charge applies, paying it as a lump sum is usually the more efficient option.
Most UK lenders let you overpay up to 10% of your outstanding balance per year without an early repayment charge (ERC); anything above that on a fixed-rate deal can trigger a fee, often 1–5% of the excess. Check your mortgage offer document or ask your lender before sending a large lump sum.
Overpaying guarantees a return equal to your mortgage rate, tax-free — hard to beat with easy-access savings unless you can get a better after-tax rate elsewhere. Keep 3–6 months of essential expenses in accessible savings first, since money paid into your mortgage isn't easily retrievable.
Most UK lenders let you choose. "Reduce term" keeps your monthly payment the same and pays the mortgage off earlier, saving the most interest overall. "Reduce payment" keeps your original end date but lowers what you pay each month. Reducing the term saves more interest for the same lump sum.
When you overpay, the extra money reduces your outstanding balance immediately. Because interest is charged on the remaining balance, a lower balance means less interest each month — which accelerates payoff further. Most fixed-rate mortgages allow up to 10% of the outstanding balance per year without early repayment charges. Tracker and variable mortgages usually have no limit.
Most UK fixed-rate mortgages allow overpayments up to 10% of the outstanding balance per year without penalties. On a £200,000 mortgage that's £20,000/year — far more than most people overpay. Above 10%, early repayment charges typically apply (1–5% of the excess). Tracker and variable rate mortgages usually have no restriction. Always check your specific mortgage terms.
Both work well. Monthly overpayments build a consistent habit and reduce the balance steadily throughout the year. Lump sums have maximum impact when paid early in the mortgage term since the capital reduction has more years to save interest. If you receive a bonus or inheritance, a lump sum early in your mortgage term is particularly powerful.
Most UK lenders keep your monthly payment the same and shorten the term — which is what this calculator models. Some lenders recalculate to reduce your monthly payment if you ask. Keeping payment the same and shortening the term saves more interest overall. You can often choose which treatment you prefer by contacting your lender.
Compare your mortgage rate to the after-tax savings rate available. If a Cash ISA pays more than your mortgage rate, saving wins. If your mortgage rate is higher, overpaying is better. Overpaying is a guaranteed, risk-free return equal to your mortgage rate. Always maintain a 3–6 month emergency fund before overpaying — mortgage money isn't easily retrievable.
Historically, global equity funds have returned 7–9% annually, well above typical mortgage rates. If your mortgage rate is below 4%, investing in an ISA is likely to win long-term. Above 5%, overpaying becomes more compelling. Between 4–5%, a split approach is sensible. Use our Invest or Overpay calculator for a precise comparison based on your specific numbers.
An offset mortgage links your savings to your mortgage — you only pay interest on the mortgage balance minus savings. Unlike overpaying, you keep access to your money. They typically carry a slightly higher rate than standard mortgages, so they're most beneficial for people with large, consistently maintained savings balances.
The most reliable method is a standing order paid alongside your normal direct debit. For lump sums, transfer directly to your mortgage account (contact your lender first to confirm the reference needed so it's allocated to capital reduction, not future installments). Always keep records of overpayments made.
This calculator is for illustrative purposes only and does not constitute financial advice. Overpayment limits, early repayment charges, and mortgage terms vary by lender. Always check your specific mortgage agreement and consult a qualified adviser before making significant overpayments.