How Much Does Making Extra Mortgage Payments Save?

Why a small overpayment saves more than it looks like it should

An overpayment comes straight off the capital you owe. Once it's credited to the balance interest is calculated on, less interest builds up going forward. Keep your payments where they are, and more of every future payment starts chipping away at the debt itself - which is what gets you to the finish line early.

£100 knocked off the balance saves about 37.5p in interest the very next month at 4.5%. Not much on its own. The real effect comes from doing that same thing, month after month, for years.

Worth being clear about what's actually happening: the overpayment itself isn't the saving. It's money you'd have paid anyway, just moved earlier. The saving is the interest you avoid by paying it sooner - minus any charges that come with doing so.

What do an extra £100, £200 or £500 a month actually save?

Starting point: £200,000 outstanding, 4.5%, 25 years left. Standard monthly repayment comes to roughly £1,111.66, with total interest over the full term at about £133,499 if you never overpay.

These figures apply interest monthly at the annual rate divided by 12, with the overpayment starting from the very first payment and continuing every month (the last payment is smaller where it needs to be). Fees and early-repayment charges aren't included, and the rate's held constant throughout. The underlying maths keeps full precision - it's just the totals and savings that get rounded to the nearest pound for display.

Want to try your own numbers? Use the overpayment options in our UK mortgage calculator and compare both the interest saved and the new payoff date against the extra you'd be committing each month.

What if you paid a £10,000 lump sum instead?

Same starting example: pay £10,000 off the balance straight away, before that month's interest accrues, and the loan drops to £190,000. Keep the original £1,111.66 monthly payment, and it clears in about 22 years 10 months - total interest falls to roughly £114,199, a saving of around £19,300.

That £10,000 hasn't vanished from what your home is costing you - you've simply paid it earlier, which stops it attracting mortgage interest for as long as it otherwise would have. Pay the same lump sum later instead, and it'll typically save less, since interest has already built up in the meantime under the same fixed-rate assumptions.

Monthly and lump-sum overpayments suit different situations. A regular surplus in your budget lends itself to monthly overpayments; a bonus or other money you already have sitting around suits a one-off payment better. Either way, compare the actual dates and figures, and check for charges before you transfer anything.

Does overpaying shorten your term, or just lower your payment?

Ask your lender directly how they'll apply it. Some recalculate your required monthly payment down, some let you reduce the term instead, and some offer a choice - it depends on your mortgage conditions. Nationwide's overpayment guidance is a good example of how this varies by product.

If your required payment drops and you only pay the new minimum, you'll get more breathing room month to month - but you won't see the earlier-payoff figures shown above. Keeping your payment where it was generally saves more interest, since the debt comes down faster. Worth checking whether maintaining that higher amount still counts toward your overpayment allowance.

And a projected earlier payoff date isn't the same thing as formally changing your contractual mortgage term - your lender can tell you exactly what gets recorded and what you're still required to pay.

Check your overpayment allowance before you pay a lump sum

A 10% annual allowance is common across UK mortgage deals, but it's not universal - the percentage, which balance it's based on, when it resets, and how regular overpayments count all depend on the specific product. Some deals are more generous; others charge you for going over. Check your mortgage offer or just ask the lender what your remaining allowance is.

As an example: a deal allowing 10% of a £200,000 balance gives you a £20,000 allowance. Go £5,000 over that, and if a 2% early-repayment charge applies to the excess, you'd be looking at a £100 charge. These are illustrative numbers, not a description of what every lender does.

Get a quote before making a large payment or clearing the mortgage entirely. What actually matters is the interest you'd avoid after any charge - including whether it's worth waiting until a charge period ends before paying.

Could overpaying help when you come to remortgage?

Bringing the balance down can improve your loan-to-value ratio. Say your home's valued at £250,000 and you owe £205,000 - that's 82% LTV. Pay off £5,000 of capital, and you're at 80%, assuming the valuation doesn't change.

That might unlock a different product band for your next deal, but a better rate isn't guaranteed - the lender's own valuation, any fees rolled into the loan, and your eligibility all still play a part. Our UK loan-to-value calculator can help you compare your balance before and after a proposed payment.

When keeping your money elsewhere makes more sense

Don't judge an overpayment purely on the headline interest saving. Expensive debts, an emergency fund, pension contributions, and costs on the horizon all matter too - and money paid into your mortgage isn't easy to get back out again. MoneyHelper's guide to paying off a mortgage early covers these competing priorities well.

Weigh the mortgage interest you'd avoid against what accessible savings could realistically earn after tax, over the same period, accounting for any fees. Investment returns carry risk and shouldn't be treated as a guaranteed substitute for interest you'd otherwise avoid paying.

And if your rate changes once a fixed deal ends, redo the sums. A constant-rate projection is a useful way to compare scenarios, but it can't tell you what your next mortgage deal will actually look like.

How to work out your own overpayment saving

1. Pull your current balance, interest rate and remaining term from your latest mortgage statement.
2. Work out a baseline with no extra payments.
3. Add whatever monthly, yearly or one-off amount you can afford in the calculator, checking when it gets applied.
4. Compare total interest and payoff date against the baseline, keeping everything else the same.
5. Confirm your allowance, any charges, and the effect on future required payments with your lender before you actually pay anything.

All of this covers repayment mortgages specifically. On an interest-only mortgage, capital overpayments still cut future interest, but you'll still need a separate plan to clear whatever's left at the end. Our guide to repayment and interest-only mortgages covers that distinction in more depth.