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How much sooner can you pay off your mortgage?
Add a monthly overpayment, a yearly lump sum or a one-off payment and see the finish date move. The charts show what you owe month by month and how much of each year's payments is interest. Then check the plan against what your lender lets you overpay, how much of that is left this year, and when it resets.
Paying £130 extra a month clears the loan 5 years 5 months sooner and saves £49,889 of interest. You put in £38,220 of extra money to get there.
What you owe, month by month
What you have paid, and what is left
Slide along the chart: at any point it shows how much you have paid so far, how much of that was interest, and what is still to come. With these overpayments you pay £433,234 in total instead of £483,123.
- Paid so far: £17,664 — £12,548 interest and £5,116 off the loan
- Still to pay: £415,569
- With no overpaying you would have paid £16,104 by now and still owe £467,019
What you pay each year
Each bar is one year of payments. As the balance falls, less of each payment is interest — and overpaying makes it fall faster, so the interest bar shrinks quicker than the dashed line (the interest you would have paid anyway).
What different overpayments do
Monthly overpayments only, on this balance and rate. Tap a row to try it above.
| Extra a month | Mortgage-free in | Sooner by | Interest saved |
|---|---|---|---|
| None | 30 years | — | — |
| +£65 | 27 years | 3 years | £28,169 |
| +£130 | 24 years 7 months | 5 years 5 months | £49,889 |
| +£340 | 19 years 3 months | 10 years 9 months | £95,891 |
| +£670 | 14 years 6 months | 15 years 6 months | £134,364 |
| +£1,300 | 9 years 11 months | 20 years 1 month | £169,034 |
Working backwards from a date
Your normal payments already finish in 30 years; pick a shorter target.
What your lender lets you overpay
In your first 12 months this plan overpays £1,560. Add the months left on your fixed deal and its early repayment charge (from your offer document) under More about your deal to see whether a charge could apply.
Allowances differ by lender in what they are measured against (current balance or original loan) and when they reset. See the verified lender rules; your offer document is the definitive statement.
Year-by-year table
| Year | Interest | Without overpaying | Repaid | Owed at year end |
|---|---|---|---|---|
| 1 | £12,548 | £12,585 | £5,116 | £240,384 |
| 2 | £12,278 | £12,399 | £5,386 | £234,997 |
| 3 | £11,993 | £12,204 | £5,671 | £229,326 |
| 4 | £11,693 | £11,998 | £5,971 | £223,356 |
| 5 | £11,378 | £11,781 | £6,286 | £217,069 |
| 6 | £11,046 | £11,552 | £6,618 | £210,451 |
| 7 | £10,696 | £11,312 | £6,968 | £203,483 |
| 8 | £10,328 | £11,058 | £7,336 | £196,147 |
| 9 | £9,940 | £10,792 | £7,724 | £188,423 |
| 10 | £9,532 | £10,511 | £8,132 | £180,291 |
| 11 | £9,102 | £10,216 | £8,562 | £171,729 |
| 12 | £8,650 | £9,904 | £9,014 | £162,715 |
| 13 | £8,174 | £9,577 | £9,490 | £153,224 |
| 14 | £7,672 | £9,232 | £9,992 | £143,233 |
| 15 | £7,144 | £8,869 | £10,520 | £132,713 |
| 16 | £6,588 | £8,487 | £11,076 | £121,637 |
| 17 | £6,003 | £8,084 | £11,661 | £109,976 |
| 18 | £5,387 | £7,660 | £12,277 | £97,700 |
| 19 | £4,738 | £7,214 | £12,926 | £84,774 |
| 20 | £4,055 | £6,745 | £13,609 | £71,165 |
| 21 | £3,336 | £6,250 | £14,328 | £56,838 |
| 22 | £2,579 | £5,729 | £15,085 | £41,753 |
| 23 | £1,782 | £5,181 | £15,882 | £25,871 |
| 24 | £943 | £4,604 | £16,721 | £9,150 |
| 25 | £145 | £3,996 | £9,150 | £0 |
Assumes a repayment mortgage at one rate for the whole period, the payment kept level, and overpayments applied to the loan straight away. Your rate will change at each deal end, so treat the dates as a guide; your lender's annual statement gives the real balance.
Why early overpayments do the most
Interest is charged on what you owe each month. A pound overpaid in year one stops earning interest for every remaining month; a pound overpaid in year twenty has little left to save. That is why the interest bars shrink faster than the dashed line, and why a one-off payment early in the loan can be worth more than the same money later.
Why the reset date is the useful part
Allowances do not carry over. If your lender resets on 1 January and you have headroom in December, that headroom expires — and a lump sum split across 31 December and 1 January can use two years' allowance in two days, entirely penalty-free. The date turns a vague "I could overpay" into a plan. Each lender's rule is on its own page in the lender rules, sourced and dated.
A watch puts your allowance reset on the same timeline as your fix end, your early-repayment-charge step-downs and your lock window, and emails you before each one. It is from £5.99, once.
Run a site or blog? The allowance calculator is free to put on your own pages — the code adds a small "Free calculator by WatchMyMortgage" link, and that's the only thing we ask for.
Frequently asked questions
How much sooner will I finish if I overpay?
It depends on the balance, the rate, the years left and how much you add. Because interest is charged on what you still owe, every pound overpaid early stops earning interest for the whole rest of the term, so early overpayments do the most work. The calculator shows the exact months saved for your numbers, and what different monthly amounts would do.
Does overpaying lower my monthly payment or shorten the mortgage?
Most lenders keep your payment the same and shorten the term, which is the default this calculator uses. Some will recalculate a lower payment if you ask. After a one-off lump sum the calculator shows both, so you can see what each does to the payment, the finish date and the interest saved.
How much can I overpay without a penalty?
Most fixed deals allow a set amount each year without an early repayment charge — often 10% — but the details differ by lender, in what it is measured against and when it resets. As published on lenders' own pages (last checked 2026-09-20): Halifax: 10% of the amount owed as at 1 January, each calendar year; Nationwide: 10% of the original loan amount, each year; NatWest: 20% of the outstanding balance, each year; Royal Bank of Scotland: 20% of the outstanding balance, each year; Santander: 10% of the fixed-rate loan, each calendar year (January to December); HSBC: 10% of the outstanding balance, each year, on the account's opening date or the fixed-rate start date; first direct: no cap — overpayments are unlimited; Virgin Money: 10% of the mortgage balance, each calendar year; TSB: 10% of the amount owed at 1 January, each calendar year; Coventry Building Society: 10% of the balance, each year. Each lender page on this site shows the source and date; your offer document states your exact rule.
When does my overpayment allowance reset?
For many lenders it is the calendar year, so it resets on 1 January; some reset on the anniversary of your deal. Unused allowance does not carry over, so the reset date is worth knowing if you have spare cash.
What happens if I overpay more than the allowance?
The excess is usually charged at your deal's early repayment charge rate — commonly 1% to 5% of the amount over the limit. On a large lump sum that can wipe out years of the interest saving, so the allowance matters. Charges normally apply only while a fixed or discounted deal is running.
Should I overpay or save the money instead?
That depends on your circumstances, and this is information rather than advice. The two things to compare are the interest rate on your mortgage and the after-tax rate you would earn on savings, along with whether you might need the cash back — money paid into a mortgage is hard to get out again. A regulated adviser can help with your own situation.
Does this calculator store my numbers?
No. Everything is calculated in your browser and nothing you type is sent to a server or stored. Your figures are held in this browser tab only, so they carry between the calculators.
Figures are estimates from the numbers you enter, using standard level-payment amortisation at one rate for the whole period. Lender rules are quoted from each lender's published pages with the date we checked them; anything we could not verify is labelled as the market assumption. Your offer document and annual statement are the definitive statements. This is information, not financial advice; for advice on your circumstances, speak to a mortgage adviser regulated by the FCA.