Guide · 4 minute read · Updated 2 Jul 2026

How much can I overpay my mortgage without penalty?

On most fixed deals, 10% of your mortgage balance per year. That figure is a market convention, not a legal right: some lenders allow 20%, some count it differently, and standard variable rate mortgages are usually unlimited. Your offer document has the exact number.

The 10% is a convention, not a law

There is no statute that grants you a 10% overpayment allowance. It is simply the term most lenders write into fixed-rate (and some tracker) deals: each year you can repay up to roughly 10% of the loan early without triggering the early repayment charge (ERC) that otherwise protects the lender's locked-in interest. Because it is contractual, it varies. NatWest, for example, allows overpayments of up to 20% of the outstanding balance per year on fixed and tracker products. At the other end, a few deals (especially some trackers and offset products) have no ERC at all, and almost every lender lets you overpay without limit once you fall onto the standard variable rate.

So the first job is not arithmetic, it is reading. Your mortgage offer document, annual statement, or the lender's app will state your allowance, the ERC schedule, and the date the allowance resets.

How lenders count the 10%

Two deals with "a 10% allowance" can permit different amounts, because lenders measure the 10% against different bases:

• Balance at the start of the year. Halifax measures 10% of the amount owed as at 1 January, with the allowance running over the calendar year. As you pay the loan down, the cash allowance shrinks each year.
• Original loan amount. Nationwide allows 10% per year of the amount you originally borrowed (for products reserved since May 2013). The cash allowance stays constant, so late in the term it can be a far bigger share of what you still owe.
• Outstanding balance, higher percentage. NatWest's 20% applies to the outstanding balance of each sub-account.

The reset date matters too: some allowances follow the calendar year, others the anniversary of your deal or your lender's own "overpayment year". Unused allowance almost never rolls over. If you are sitting on a lump sum near the reset date, splitting it across two allowance years can double what you can pay penalty-free.

Also check what an overpayment does by default. Most lenders, like the mortgage overpayment calculator, keep your monthly payment the same so the extra shortens the term, which is where the big interest savings come from; some instead recalculate a lower payment unless you ask otherwise. The mortgage repayment calculator shows how much of each payment is interest, which is the money overpaying actually attacks.

ERC percentages step down with the fix

ERCs typically run between 1% and 5%, and on most fixed deals they step down each year of the fix. A common shape on a five-year fix is 5% in year one, then 4%, 3%, 2%, and 1% in the final year; a two-year fix might be 2% then 1%. The longer your lock and the earlier you break it, the bigger the percentage.

What the percentage applies to depends on what you do. Overpay beyond your allowance and most lenders (Halifax and NatWest say so explicitly) charge the ERC only on the excess above the allowance. Redeem the whole mortgage early, by selling without porting or remortgaging mid-fix, and the ERC applies to the whole balance repaid, which is where the genuinely painful numbers live.

What a breach actually costs: a worked example

Say you owe £250,000 at 4.5% with 20 years left, in year two of a five-year fix with a 5-4-3-2-1 ERC ladder, and a 10% allowance measured on this year's balance (£25,000). An inheritance lands and you want to pay in £40,000.

Pay it all at once and you breach by £15,000. At year two's 4%, the ERC is £600. That is annoying but not catastrophic: the £40,000 lump sum saves about £48,460 of interest and clears the mortgage roughly four and a half years early.

The smarter move is usually to split: £25,000 now (saving about £32,420 of interest by itself) and £15,000 the day the allowance resets. The cost of waiting is only the gap between your mortgage rate and your savings rate on £15,000 for a few months. If that gap is around half a percentage point, six months of waiting costs roughly £37, against the £600 ERC. Only if your reset is far away or your savings rate is poor does paying the penalty start to look reasonable.

Contrast that with full redemption: clearing the entire £250,000 in year two costs 4% of the lot, £10,000. That is why people port their mortgage or time a move to the end of the fix rather than simply paying it off.

Before you overpay at all

Penalty-free does not automatically mean sensible. Clear expensive debt first, keep an emergency fund (overpaid money is very hard to get back out), and weigh the mortgage rate against what savings or pension contributions would earn; our overpay or save guide walks through that comparison. Then run your own numbers in the mortgage overpayment calculator before sending anything.

Common questions

What happens if I overpay my mortgage by more than 10%?

You trigger your deal's early repayment charge, but most lenders only apply it to the amount above the allowance, not the whole overpayment. On a £15,000 excess at a 4% ERC that is £600. Check your offer document, because both the allowance and the charging basis vary by lender.

Does the 10% overpayment allowance apply to the original loan or the current balance?

It depends on the lender. Halifax uses 10% of the balance owed at 1 January each year, Nationwide uses 10% of the original loan amount, and NatWest allows 20% of the outstanding balance. The same headline rule can mean different cash amounts, so check how yours is measured and when it resets.

Can I overpay as much as I like on a standard variable rate mortgage?

Usually yes. SVR mortgages almost never carry early repayment charges, so overpayments are typically unlimited. Many tracker deals are also unrestricted, though some have ERCs during an initial period, so confirm before paying in a lump sum.

Do early repayment charges reduce each year of a fixed deal?

On most deals, yes. ERCs typically run from 1% to 5% and step down annually, for example 5% in year one of a five-year fix falling to 1% in the final year. A few deals charge a flat percentage for the whole fix, so read the ERC schedule in your offer.

Is it better to overpay monthly or as a lump sum?

Mathematically, earlier money saves more interest, so a lump sum now beats the same total drip-fed later. In practice both work well, and monthly overpayments are easier to keep inside the annual allowance. If a lump sum would breach it, split the payment around your allowance reset date.

Guidance and education, not regulated financial advice.