How much does a £200/month overpayment actually save?

Take the calculator's own default case: a £200,000 mortgage at 4.57%, 25 years remaining, roughly in line with average fixed rates this year (Moneyfacts, July 2026). On the standard schedule alone, you'd pay around £1,120 a month and hand over roughly £136,000 in interest by the time the mortgage is cleared. Add a £200 monthly overpayment and the maths shifts more than most people expect.

The £200,000 example, run through the calculator

Loan £200,000 at 4.57% over a 25-year term: standard monthly payment is about £1,120, total interest roughly £136,000. Add a £200/month overpayment (new monthly outgoing £1,320) and the mortgage clears in around 18 years 10 months (about 6 years 2 months early), with total interest of roughly £98,300. That's a saving of close to £37,700 in interest for £200 a month.

Run the same loan through our mortgage repayment calculator first if you want to see your baseline payment before adding an overpayment on top: it's the same underlying figures, without the extra scenario.

Put simply, £200 a month on a typical UK mortgage can wipe out six years and tens of thousands of pounds in interest, which changes how you should weigh it against other monthly outgoings.

Why does overpaying early save more than overpaying later?

A mortgage charges interest on whatever balance is still outstanding, so every pound you shave off the balance in year one keeps earning you interest savings for the full remaining term. The same pound taken off in year twenty only has a few years left to work. This is why financial advisers and mortgage brokers consistently point people toward overpaying as early as possible rather than "getting round to it" once other spending pressures ease.

In practical terms, £200 a month started from day one of a 25-year term saves considerably more in total interest than the identical £200 a month started ten years in, even though the total amount overpaid over the life of the mortgage is smaller in the first case. Front-loading beats back-loading, every time.

If you're weighing up overpaying now versus waiting until your income rises, the maths points toward starting small and early rather than saving up for a bigger overpayment later: delay costs you the compounding, not just the money.

What's the 10% overpayment limit, and what happens if I go over it?

Most UK lenders cap penalty-free overpayments at around 10% of the outstanding balance per year on fixed-rate deals (Moneyfacts, 2026). On a £200,000 balance, that's roughly £20,000 a year, or about £1,667 a month, before an Early Repayment Charge (ERC) kicks in. This is typically a percentage of the amount over the limit, sometimes running to several thousand pounds depending on the deal and how far through the fixed term you are.

A £200 monthly overpayment sits comfortably inside that allowance for almost any mortgage size, which is why it's a realistic example. Where people come unstuck is lump-sum overpayments (a bonus, an inheritance, or downsizing proceeds) pushed in all at once without checking the annual limit first. The calculator models whatever figure you enter, but it doesn't know your lender's specific cap, so that check has to happen separately, against your actual mortgage offer or annual statement.

Before you commit to any regular overpayment above a token amount, check your own offer document for the exact percentage and reset date. Assuming 10% applies to your deal without confirming it is the single most common way people accidentally trigger an ERC.

Should I overpay the mortgage or use that money elsewhere?

Overpaying is effectively a guaranteed, tax-free return equal to your mortgage rate. At 4.57%, that beats most easy-access savings rates after tax and sits close to top fixed-rate savings bonds (Moneyfacts, July 2026). Where overpaying loses out is against a workplace pension with employer matching, since that match is free money no mortgage overpayment can replicate, and against building an emergency fund, since equity locked into your home isn't accessible if your boiler fails or your income drops. Most people who run these numbers end up doing a mix: keep three to six months of costs liquid, take any available employer pension match in full, and put genuinely spare income toward the mortgage rather than a low-interest savings account.

If you've already got an emergency fund and any pension match is being claimed in full, the remaining spare income is a straightforward call in favour of overpaying at current mortgage rates rather than parking it in an average savings account.

What this means for you

Two things the calculator can't do for you: check your lender's actual overpayment allowance, and account for the fact your rate almost certainly won't stay fixed for the whole remaining term. Most borrowers remortgage every two to five years, so the interest-rate assumption here is a simplification, not a forecast.

Use the tool to size the opportunity: the scale of the saving is the useful output, even if the exact figure shifts once you remortgage. If your fixed deal has under a year left to run, it's worth reading our remortgage prep guide alongside this calculator, since the rate you secure next will matter more to your total interest bill than fine-tuning this month's overpayment amount.

For most people carrying a standard residential mortgage with spare income and no higher-priority debt, the maths points toward a modest, regular overpayment started as early as possible, rather than a large one-off that risks breaching your lender's annual cap.