Mortgage Overpayment Calculator

See how much sooner you’ll pay off your mortgage, and how much interest you’ll save, by paying extra each month or a lump sum.

Mortgage balance

What you owe now

Interest rate

Years left

Monthly overpayment

One-off lump sum

Paid now

Mortgage-free sooner by

4 years

Paid off in 16 years instead of 20 years

Interest saved: £22,936
Monthly repayment with extra: £1,465.30

Interest you’ll pay£80,735
Interest saved£22,936

What this means

Every extra repayment goes straight off what you owe, so you stop paying interest on it. That’s like a guaranteed return of 4.5%, your mortgage rate.

Clear debts with higher rates, like credit cards, first, and keep an emergency fund before overpaying. Check your lender’s limits on overpayments without a fee.

Next step

Compare with saving it instead

With and without overpaying

	Without	With
Monthly repayment	£1,265.30	£1,465.30
Lump sum now	–	–
Time left	20 years	16 years
Total interest	£103,672	£80,735
Total paid	£303,672	£280,735

Before you overpay

Many fixed-rate mortgages let you overpay up to 10% of the balance each year without an early repayment charge. Check your mortgage offer before paying more.

Keep some savings for emergencies first. And if your savings earn more after tax than your mortgage rate, saving can beat overpaying.

£17,584£8,792£0

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PrincipalInterest

Assumptions in this estimate

Your repayment stays the same, so overpaying shortens the mortgage. Some lenders lower your repayment instead, which saves less interest.
Assumes the interest rate stays the same for the rest of the mortgage.
Fees or charges for overpaying aren’t included.

Spotted a mistake? Tell us

How the calculator works

Your mortgage now: what you owe, the rate and the years left give your current repayment.
Paying extra: an extra amount with every repayment, a one-off lump sum, or both. Your repayment stays the same, so the mortgage ends sooner.
The difference: how much sooner it’s paid off, and the interest you save.

Example

£200,000 at 4.5% with 20 years left, repaid at £1,265.30 a month:

Paying extra	Paid off in	Interest saved
Nothing	20 years	–
£200 a month	16 years	£22,936
£500 a month	12 years, 4 months	£42,796
£10,000 lump sum	18 years, 6 months	£13,746

Last updated October 14, 2026

Frequently asked questions

How much will I save by paying £200 extra a month?

On a £200,000 mortgage at 4.5% with 20 years left, £200 extra a month clears it 4 years sooner and saves £22,936 in interest.

Is a lump sum or extra each month better?

Both help, and the sooner money goes in, the more interest it saves. On the same mortgage, a £10,000 lump sum now clears it 1 year, 6 months sooner and saves £13,746.

How much can I overpay without a charge?

Many fixed-rate mortgages let you overpay up to 10% of the balance each year. Paying more can mean an early repayment charge, so check your mortgage offer. Standard variable rates usually have no limit.

Should I pay off my mortgage or save?

Keep some savings for emergencies first. After that, if your savings earn more after tax than your mortgage rate, saving can come out ahead.