Lump Sum vs Monthly Mortgage Overpayments: Which Saves More Interest?
You have £10,000 and a mortgage. Do you pay it all off in one go, or feed it in at £200 a month? And if you overpay out of your salary, is it smarter to save up and make one big annual payment? The answer comes down to a single idea, when each pound reaches the mortgage, but the size of the difference, and the situations where the usual answer flips, are worth knowing before you ring your lender. Here are the numbers on a typical £200,000 UK mortgage.
Published: 24 September 2026 at 09:00 · 7 min read
The Short Answer
Money in hand: pay the lump sum. Money from income: overpay monthly. A pound on your mortgage stops being charged interest the moment it arrives, so the earlier it gets there, the more it saves. On a £200,000 mortgage at 4.5% over 25 years (standard payment £1,112 a month), overpaying from the start with the term reduced:
- A £10,000 lump sum on day one saves about £19,300 of interest and clears the mortgage 2 years 2 months early.
- The same £10,000 fed in at £200 a month over just over four years saves about £16,900 and clears it 2 years early.
- Saving £200 a month from your salary for four years and then paying it as one lump sum saves only about £15,700, even after adding the interest earned in a 4% savings account.
Neither method is magic. The lump sum wins in the first case and loses in the third for the same reason: timing. The rest of this guide shows how big the gaps are, when they matter, and the practical limits (early repayment charges and access to your cash) that can outweigh the maths.
You Have £10,000 Now: Lump Sum or Drip-Feed?
This is the windfall situation: a bonus, an inheritance, or savings above your emergency fund. The instinct to drip-feed it “to be safe” is understandable, but the pounds you have not yet paid in sit in a savings account earning less than your mortgage costs. The table compares the options on the £200,000, 4.5%, 25-year example, assuming the undeployed cash earns 4% and that interest is also paid onto the mortgage.
| How the £10,000 is used | Interest saved | Mortgage cleared in | vs lump sum |
|---|---|---|---|
| £10,000 lump sum on day one | £19,300 | 22.8 years | – |
| £200/month, rest in 4% savings (no tax) | £18,100 | 22.8 years | −£1,200 |
| £200/month, savings taxed at 20% | £17,900 | 22.9 years | −£1,400 |
| £200/month, savings taxed at 40% | £17,600 | 22.9 years | −£1,700 |
| £200/month, rest earning nothing | £16,900 | 23.0 years | −£2,400 |
The lump sum wins in every row, by between £1,200 and £2,400. That is a real but not enormous gap on a £10,000 decision, and it is the price of keeping some of the money accessible for four years. Whether savings interest is taxed depends on your Personal Savings Allowance (£1,000 for basic-rate taxpayers, £500 for higher-rate), so most people drip-feeding a single £10,000 would pay little or no tax on it. The gap grows with the size of the lump sum: £20,000 on day one saves about £36,000, against £31,500 for £400 a month over the same period, a difference of roughly £4,400 before savings interest.
The underlying rule is worth remembering: any pound sitting in cash earning less (after tax) than your mortgage rate is costing you the gap. At 4.5% on the mortgage and 4% gross on savings, the gap is small; at 5.5% on the mortgage and 3% on savings, it is substantial.
Overpaying From Your Salary: Monthly or Save Up for a Lump Sum?
Most overpayments are not windfalls; they are whatever is left at the end of the month. Here the question is whether to send £200 to the lender each month or build it up in a savings account and pay periodically. Same £200,000 mortgage at 4.5%, £10,000 overpaid in total over just over four years, savings earning 4%:
| Approach | Interest saved | vs monthly |
|---|---|---|
| £200 every month | £16,900 | – |
| Save up, pay £2,400 once a year | £16,650 | −£250 |
| Save up for four years, pay one £10,860 lump sum | £15,700 | −£1,200 |
Monthly wins, but an annual lump sum costs only about £250 over the life of the mortgage. That is small enough that behaviour should decide it. If a standing order is the only way the money reliably ends up on the mortgage, go monthly. If you prefer to keep a year’s overpayments in an easy-access account as an extra buffer and pay them in each January or on your deal anniversary, the cost of that flexibility is modest. What does get expensive is “saving up for a big payment” that keeps being postponed: four years of waiting costs about £1,200, and the pot has a habit of being spent on something else.
How Does the Mortgage Rate Change the Gap?
The higher your rate, the more a lump sum is worth and the more it costs to wait. Same £200,000, 25-year mortgage, £10,000 overpaid from the start in three different ways (no savings interest on money waiting):
| Mortgage rate | £10k lump sum now | £200/month for 4 years | £10k lump sum after 4 years |
|---|---|---|---|
| 3.5% | £13,200 | £11,700 | £10,100 |
| 4.5% | £19,300 | £16,900 | £14,500 |
| 5.5% | £26,900 | £23,300 | £19,700 |
| 6.5% | £36,200 | £31,000 | £26,000 |
At 3.5% the gap between paying now and paying in four years is about £3,100; at 6.5% it is over £10,000. Timing matters just as much later in the term, though the totals are smaller: a £10,000 lump sum in year 10 of the 4.5% example saves about £9,000, against £7,400 for £200 a month started at the same point. For how the overpayment amount itself changes the result, see our £100, £200 and £500 a month worked examples.
When Does a Lump Sum Not Make Sense?
The maths favours getting money onto the mortgage early, but three practical limits can outweigh it.
1. It would breach your overpayment allowance
Most UK fixed and tracker deals allow 10% a year penalty-free, about £20,000 on a £200,000 mortgage. A lump sum above that usually attracts an early repayment charge on the excess, typically 1–5% depending on the year of the deal. A £25,000 lump sum in year one of a five-year fix at 5% would cost about £250 on the £5,000 excess, which is more than the extra interest the excess would save before the allowance resets. The better move is usually to pay up to the allowance now and hold the rest until the reset date, or until your deal ends and you move to the standard variable rate, where overpayments are normally unlimited. Our 10% overpayment rule guide covers how lenders measure the allowance, and the early repayment charge guide shows when paying an ERC is still worth it. Regular monthly overpayments almost never come close to the limit, which is one of their quiet advantages.
2. You might need the money back
A lump sum on a standard repayment mortgage is gone. Getting it back means applying for further borrowing, subject to affordability checks and the lender’s appetite at the time. Keep an emergency fund of three to six months’ spending in cash or Premium Bonds before any large overpayment. If you want to reduce interest while keeping the money reachable, an offset mortgage does exactly that, though offset rates are usually a little higher. Drip-feeding a windfall is a reasonable compromise if you are unsure about job security: the table above shows the cost is around £1,200–£1,700 on £10,000.
3. Your cash earns more than your mortgage costs
If you locked in a 1.5% fix in 2021 and easy-access savings now pay 4%, holding the money in savings and paying a lump sum when the fix ends is the better trade, especially if the savings interest falls within your Personal Savings Allowance. The same logic makes a Stocks & Shares ISA or pension contribution a strong competitor to any overpayment; our pay off the mortgage or invest guide runs that comparison, and overpayments and your FIRE date shows the effect on when you can stop working.
How to Make a Lump Sum Overpayment Count
- Ask for the term to be reduced, not the payment. Many lenders default to recalculating your monthly payment after a lump sum, which keeps the mortgage running for the full term and gives back much of the saving.
- Check your allowance and reset date first. Know whether the 10% is measured on the original loan or the current balance, and whether it resets on 1 January or your deal anniversary. Straddling the reset lets you pay two years’ allowances within a few weeks.
- Pay promptly. Most UK lenders now calculate interest daily, so the saving starts the day the money lands. Leaving a bonus in a current account for months while you decide is the most common way lump sums lose value.
- Combine both methods. They are not either/or. Adding a £10,000 lump sum on top of £200 a month on the example mortgage brings the mortgage-free date forward from about 18.9 years to 17.4 years and saves roughly £12,600 more interest than the monthly overpayments alone.
- Get confirmation in writing. Check your next statement or online account shows the reduced balance and the new end date. The MoneyHelper overpayment guide is a useful independent checklist.
Frequently Asked Questions
Is it better to overpay a mortgage monthly or as a lump sum?
If you already have the money, a lump sum saves more, because every pound starts cutting interest straight away. On a £200,000 mortgage at 4.5% over 25 years, a £10,000 lump sum at the start saves about £19,300 of interest, while drip-feeding the same £10,000 as £200 a month over four years saves about £16,900. If the money comes from your salary each month, the opposite is true: overpaying £200 every month saves slightly more than saving it up and paying an annual lump sum, because the money reaches the mortgage sooner. The rule is simple: get each pound onto the mortgage as early as you can, within your penalty-free allowance.
How much does a £10,000 lump sum save on a mortgage?
On a £200,000 repayment mortgage over 25 years, a £10,000 lump sum paid at the start saves about £13,200 of interest at 3.5%, £19,300 at 4.5%, £26,900 at 5.5% and £36,200 at 6.5%, and cuts roughly two to three years from the term, as long as the lender reduces the term rather than the monthly payment. Paid in year 10 instead of year one, the same £10,000 at 4.5% saves about £9,000, because there is less of the term left for the reduced balance to save interest over.
Should I save up and pay a lump sum off my mortgage once a year?
Usually not, unless your savings account pays more after tax than your mortgage costs. Saving £200 a month in a 4% account and paying it off the mortgage once a year saves about £16,650 of interest on a £200,000 mortgage at 4.5%, against about £16,900 for paying £200 every month, so annual lump sums cost about £250. Saving for four years and paying one larger lump sum costs about £1,200. The exceptions are when your mortgage rate is lower than what you can earn on cash after tax, or when you want to hold the money as an emergency fund until you are sure you will not need it.
Will a lump sum mortgage overpayment trigger an early repayment charge?
It can. Most UK fixed and tracker deals let you overpay up to 10% of the balance or original loan each year without an early repayment charge. On a £200,000 mortgage that is about £20,000 a year. Any lump sum above the allowance is typically charged at the deal’s ERC rate, often 1–5%, on the excess. A £25,000 lump sum in year one of a five-year fix with a 5% ERC would cost about £250 on the £5,000 excess. Regular monthly overpayments rarely hit the limit, which is one practical advantage they have over large lump sums.
Can I get a lump sum overpayment back if I need it?
Usually not. On a standard UK repayment mortgage an overpayment reduces your balance permanently, and getting the money back means applying to borrow more, which is subject to affordability checks and may not be approved. Some flexible mortgages allow payment holidays or borrow-back of overpayments, and an offset mortgage lets you reduce interest while keeping savings accessible. Make sure you have an emergency fund of three to six months of spending before putting a large lump sum into your mortgage.
Work Out Your Own Numbers
Your balance, rate and remaining term will differ from the example, so test both approaches on your own mortgage:
- Mortgage Overpayment Calculator — enter your balance, rate and term, then compare a one-off lump sum with a regular monthly overpayment to see the interest saved and the new mortgage-free date
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