How Much Can You Overpay on Your Mortgage Without a Penalty? The 10% Rule

What Is the 10% Overpayment Rule?

During a fixed, tracker or discounted deal, most UK lenders let you overpay up to 10% of your mortgage each year with no early repayment charge (ERC). This is the “annual overpayment allowance”. Anything you overpay above it during the deal period attracts the ERC, which is typically 1–5% of the excess, as our guide to early repayment charges explains.

The 10% is not a legal rule. It is simply the market convention, and it is not universal. A handful of lenders and products allow 20%, a few older deals were capped at a fixed monthly sum such as £500, and once your deal ends and you move to the lender’s standard variable rate (SVR), or if you are on a no-ERC tracker, you can usually overpay as much as you like.

On a £200,000 mortgage, a 10% allowance is £20,000 a year, or roughly £1,667 a month. That is more than the vast majority of borrowers could ever overpay from income, which is the first thing to understand: for regular monthly overpayers the allowance is almost never a constraint. It only matters when a lump sum arrives, whether a bonus, an inheritance, a house-sale surplus or a maturing investment, and that is exactly when the small print starts to count.

How Is the 10% Measured?

Three questions decide what your allowance is actually worth in pounds, and they are all answered in your mortgage offer or Key Facts Illustration.

• 10% of the original loan, or of the current balance? Lenders that use the original amount borrowed give you a fixed allowance for the whole deal: £20,000 every year on a £200,000 loan. Lenders that use the balance outstanding at the start of each year give you a shrinking allowance, because every payment, regular or extra, reduces the figure the 10% is applied to.
• Calendar year or deal anniversary? Some lenders reset the allowance on 1 January. Others reset it on the anniversary of the mortgage completing or the deal starting. Unused allowance is lost at the reset, and it never carries forward.
• Do regular overpayments count? At almost every lender, yes. Your monthly overpayments and any lump sums are added together against the same annual limit. Only a small number of products exclude modest regular overpayments from the calculation.

Here is how the allowance evolves on a £200,000 mortgage at 4.5% over 25 years under the two measurement bases. The middle column assumes you make only the normal £1,112 monthly payment; the right-hand column assumes you use the full allowance every year, which is where the two bases diverge sharply.

For a normal borrower the gap between the two bases is a few hundred pounds a year and rarely matters. For someone aggressively clearing a mortgage on the way to FIRE it matters a great deal: on the balance basis, using the full allowance every year clears the £200,000 loan in 10.3 years, while on the original-loan basis the same discipline clears it in 6.8 years, because the allowance never shrinks. If you expect to overpay heavily, the measurement basis is worth checking before you choose a lender, not after.

How Do the Main UK Lenders Measure the 10%?

Lenders change their terms, and older products often differ from what is sold today, so treat the table below as a guide to the typical approach at each lender rather than a description of your specific deal. Your mortgage offer and your annual statement are the only documents that count.

Two practical points follow. First, the calendar-year lenders create a useful quirk: a lump sum paid in late December and another in early January uses two years’ allowance within days. Second, if you have several sub-accounts (common after a further advance or a product transfer), the allowance is usually calculated per sub-account, so a lump sum may need to be split. The government-backed MoneyHelper guide to overpaying is a sensible independent cross-check on your own lender’s terms.

What Does a 10% Allowance Actually Let You Do?

On a £200,000 mortgage at 4.5% over 25 years, the standard payment is £1,112 a month and the total interest over the term is about £133,500. Here is what different overpayment levels do, and how much of the allowance each one uses:

The message is that the allowance is generous. Even £1,000 a month, which would clear the mortgage in under a decade, uses only 60% of it. Someone overpaying £500 a month still has around £14,000 of headroom each year for a bonus or windfall. In practice the 10% rule only becomes a binding constraint for people receiving large lump sums, and for the FIRE crowd deliberately trying to be mortgage-free in five to seven years. For everyone else, the more important decision is whether overpaying beats investing at all, which our pay off the mortgage or invest guide covers.

What Happens If You Go Over the 10%?

You pay the early repayment charge, and at most lenders it applies only to the excess above the allowance. Suppose you receive a £25,000 bonus in the first year of a five-year fix with a 5% ERC, and your allowance is £20,000. Overpaying the lot costs 5% of the £5,000 excess: £250.

Is that worth paying? The £5,000 excess saves about £225 of mortgage interest in the year you would otherwise wait. Parked in an easy-access account at 4% it earns £200 gross, around £160 after basic-rate tax or £120 for a higher-rate taxpayer once the Personal Savings Allowance is used. So the true cost of waiting twelve months for the allowance to reset is £65–£105, well under the £250 charge. The same logic applies at almost any ERC rate above 1%: hold the excess in savings and pay it in the day the allowance resets. If the money would otherwise go into a Stocks & Shares ISA, the case for waiting is stronger still.

There are two traps. A minority of lenders charge the ERC on the whole overpayment, not just the excess, if a single payment takes you over the limit, which turns a £250 charge into £1,250. And some lenders count an overpayment against the allowance in the year it is received, so a payment that lands on 2 January rather than 30 December belongs to a different year. Keep each payment comfortably inside the line, and confirm the date it will be applied before you send a large one.

How to Use Every Pound of Your Allowance

• Find your reset date and measurement basis. Both are in your mortgage offer and usually on your annual statement. If you cannot find them, ring the lender and ask for the overpayment allowance remaining this year; most will tell you the exact figure.
• Ask for the term to be reduced, not the payment. Many lenders default to recalculating your monthly payment downwards after an overpayment, which quietly hands back most of the benefit. Choose to keep the payment the same and shorten the term, or the overpayment barely moves your mortgage-free date.
• Add up regular and lump-sum overpayments. If you overpay £500 a month you have used £6,000 before any lump sum. Work out the headroom left before a bonus lands, not after.
• Straddle the reset with big lump sums. A £40,000 windfall on a calendar-year lender can go in as £20,000 in late December and £20,000 in early January with no charge at all. On an anniversary lender, do the same either side of the anniversary.
• Use the SVR window between deals. The gap between one deal ending and the next starting is charge-free and unlimited. If a large sum is available, overpay it then, before the new fix begins, and take a smaller new loan.
• Park the excess somewhere useful. Anything above the allowance should sit in a savings account, Premium Bonds or an ISA until the reset, rather than paying an ERC. It is not idle money; it is next year’s overpayment earning interest.
• Consider an offset mortgage if you expect regular lump sums. Offsets have no overpayment allowance to manage, because savings sit against the balance rather than reducing it, and the money stays accessible. The rate is usually higher, so this suits people with large cash balances rather than most borrowers.
• Re-check when you remortgage. A new product can carry a different allowance, basis and reset date. If overpaying is central to your plan, weigh a 20% or original-loan-basis product against one with a slightly lower rate.

For FIRE planning, the allowance is best treated as a ceiling you sequence around rather than a target to hit. Fill it when it is cheap to do so, put the surplus into your ISA or pension where it grows tax-free, and revisit the split each year. Our guide to how overpayments move your FIRE date shows how the mortgage-versus-investing balance plays out over a decade.

Frequently Asked Questions

Work Out Your Own Numbers

See what your allowance is worth before you decide how much to overpay:

• Mortgage Overpayment Calculator — enter your balance, rate and term to see the interest saved and years cut from any monthly overpayment or lump sum up to your allowance
• Principal Payback Calculator — model doubling up on the capital portion of each payment and check it stays inside your 10%