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ClearMoney Calcs

Mortgage Overpayment Calculator (UK)

Enter your mortgage balance, rate and years left, then a regular monthly overpayment, a one-off lump sum or both, to see your new end date, the months and interest you'd save and how your balance falls year by year.

  • Updated
  • Formula tested
  • Private: runs in your browser

Your mortgage

Paid now

Interest saved

£36,281

Mortgage-free 6 years 1 month sooner

New end date

18 years 11 months

Instead of 25 years

Months saved

73

227 payments left instead of 300

Monthly payment

£1,111.66

Before overpayments

Total interest

£97,220

vs £133,501 without overpaying

First-year overpayments: 1.2% of the balance. Many lenders allow up to 10% a year without a charge; check your lender.

Balance by year

What you’d still owe at the end of each year, with and without overpaying.

Results are estimates for educational purposes and are not financial advice.

How to use this mortgage overpayment calculator

  1. Mortgage balance: what you owe today.
  2. Interest rate and years left: from your latest statement.
  3. Monthly overpayment: a regular amount you'd pay on top of your normal payment.
  4. One-off lump sum: a single payment now, for example from savings or a bonus. Leave either at 0 if you only want the other.

You'll see the interest you'd save, your new mortgage-free date, the months saved and a chart of your balance year by year with and without overpaying.

How the saving is worked out

Because interest is charged on what you owe, every pound of overpayment stops costing interest straight away and for the rest of the mortgage. That's why overpaying early in a mortgage has the biggest effect.

Worked example

A one-off £10,000 lump sum instead would save £19,300.83 and cut 26 months. Doing both, £200 a month plus £10,000 now, would bring the mortgage down to 210 payments and save £48,930.11 in interest.

Check your lender's overpayment allowance

Many lenders allow you to overpay up to 10% of the balance each year without an early repayment charge, but the limit, how the year is counted and whether lump sums and regular overpayments are treated the same vary between lenders. On some deals you can overpay as much as you like. The calculator shows what share of your balance you'd overpay in the first year and flags it if that's over 10%: check your lender before going above your allowance, because the charge could cancel out part of the saving.

Overpaying vs saving

Overpaying is effectively a guaranteed return at your mortgage rate. Savings accounts pay a different rate, and interest on savings can be taxed. But there are good reasons not to put every spare pound into the mortgage:

  • Keep an emergency fund. Money paid into a mortgage usually can't be taken back out easily.
  • Clear expensive debts first. Credit cards and personal loans usually charge more than a mortgage.
  • Consider pension contributions. Tax relief and any employer contributions can make them worth more than overpaying.

Ways to overpay

  • Regular overpayments by standing order, set up through your lender.
  • Lump sums from savings, a bonus or an inheritance.
  • Keeping your payment the same after remortgaging to a lower rate: the difference works as an overpayment.

Ask your lender to confirm that overpayments reduce the balance (rather than being held as a payment in advance) and whether they shorten the term or lower the payment.

To compare a new deal with your current one, try the remortgage calculator. For payments on a new mortgage, use the UK mortgage calculator, or the first-time buyer mortgage calculator if you're buying your first home.

What this calculator doesn't include

The calculator assumes your rate stays the same until the mortgage is paid off, your monthly payment doesn't change and overpayments are applied to the balance straight away. It doesn't include early repayment charges, rate changes when a deal ends or the effect of remortgaging. Use it to compare options, then check the details with your lender.

How much difference does the amount make?

Using the same £200,000 mortgage at 4.5% with 25 years left, each extra pound you overpay saves more interest the earlier you pay it. A regular monthly overpayment works because it keeps reducing the balance every month for years, and each reduction means a little less interest the next month. That compounding effect is why £200 a month, which adds up to £2,400 a year, saves far more than £2,400 of interest over the life of the mortgage.

A lump sum works the same way but all at once. Paying £10,000 now removes the interest that £10,000 would have built up over the remaining term. If you're choosing between a lump sum now and the same total spread over the next few years, paying sooner usually saves more, as long as you keep enough savings for emergencies.

Try a few amounts in the calculator to find a level you can keep up. A smaller overpayment you can afford every month often achieves more than a larger one you have to stop.

Overpaying on a fixed or tracker rate

On a fixed-rate deal, the overpayment allowance usually applies for the length of the deal, and paying more than the limit can trigger an early repayment charge. On a tracker or standard variable rate, some lenders allow larger or unlimited overpayments, but check your own terms. If your rate changes, the interest you save changes too: the calculator assumes today's rate for the whole term, so treat the result as an estimate and rerun it when your rate changes.

Frequently asked questions

How much can I overpay my mortgage without a penalty?

Many lenders allow overpayments of up to 10% of the balance each year without an early repayment charge, but the limit and how it's measured vary. Check your mortgage offer or ask your lender before overpaying more.

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

Money paid earlier saves more interest, so a lump sum now saves more than the same amount spread over later months. A regular monthly overpayment can save even more in total because it keeps going for years. The calculator lets you try either or both.

Does overpaying reduce my monthly payment or my term?

This calculator assumes your monthly payment stays the same, so overpayments shorten the term. Some lenders instead recalculate the payment so it falls while the term stays the same. Ask your lender which they do, or whether you can choose.

Should I overpay my mortgage or save the money?

Overpaying saves interest at your mortgage rate, while savings earn interest at the savings rate, usually taxed. Many people keep an emergency fund first and overpay with money they won't need soon, because getting it back out of the mortgage can be difficult.

What happens to overpayments when I remortgage?

They've already reduced your balance, so you'll borrow less on the new deal, which can lower your payment or put you in a better loan-to-value band. The overpayment allowance usually resets with the new deal's terms.

How is the interest saved worked out?

The calculator runs your mortgage month by month twice: once with your normal payment and once with your overpayments. Interest each month is the balance times your rate divided by 12. The difference in total interest is your saving.

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