Skip to the tool

Mortgage overpayment calculator

A spare £100 a month against the mortgage buys more than it looks like. This shows exactly what: interest saved and years removed.

Guide

How to use it

  1. Enter your mortgage as it stands: outstanding-ish price and deposit (or price minus deposit equal to your balance), rate and remaining term.
  2. Set the monthly overpayment you are considering.
  3. Read the headline: interest saved and time cut. The table shows the balance falling faster year by year.
  4. Before setting up the payment, check your deal’s early repayment charge, most fixes allow 10% of the balance per year penalty-free.

Examples

What overpaying buys

£100/MONTH

On the default £255,000 loan at 4.5% over 25 years, £100 extra a month saves roughly £23,000 of interest and finishes about 3 years early. The pound signs compound in your favour for once.

LUMP VS MONTHLY

A £12,000 lump sum now beats £100 a month for ten years, earlier money works longer. Model a lump by reducing the price/deposit gap and comparing.

OVERPAY VS SAVE

Overpaying "earns" your mortgage rate, tax-free and risk-free. Beat it only if savings pay more after tax, or if you lack an emergency fund, build that first, it outranks everything.

Method

How it works

The calculator runs the amortisation twice, with and without the extra payment, and reports the difference in total interest and in months to zero. Overpayments go entirely against principal, which is why their effect compounds: every pound repaid stops earning interest against you for the rest of the term.

Early repayment charges are the one catch: inside a fixed or discounted period, lenders typically cap penalty-free overpayment at 10% of the balance a year. The calculator does not model ERCs, check your offer document before committing.

FAQ

Frequently asked questions

Is overpaying always worth it?

After an emergency fund and any employer pension match, usually, it is a guaranteed, tax-free return at your mortgage rate. High-interest debts (cards, loans) should be cleared first, they cost more than the mortgage saves.

Monthly overpayments or a lump sum?

Earlier is better, so a lump now beats the same total dripped. But regular overpayments are behaviourally easier and most deals allow them freely within the 10% cap.

Will my lender reduce the payment or the term?

Ask for the term, keeping your payment the same is the whole point. Some lenders default to reducing the payment, which quietly undoes the benefit.

What is an early repayment charge?

A percentage fee (commonly 1 to 5%, stepping down through the fix) on overpayment beyond the allowance. Time big lump sums for the fix’s end if the ERC would bite.

Can I stop overpaying if money tightens?

Voluntary overpayments stop whenever you like. That flexibility is an argument for overpaying rather than shortening the contractual term at remortgage.

Does overpaying help me remortgage?

Yes, a lower balance means a lower loan-to-value band, which unlocks cheaper rates at the next deal. The saving compounds twice.

More tools

Related tools

Mortgage calculatorThe base payment first. Compound interestThe same force, working for you. Stamp duty calculatorMoving instead? Price the tax. Take-home payFind the spare £100.
Skip to the tool

Mortgage overpayment calculator

A spare £100 a month against the mortgage buys more than it looks like. This shows exactly what: interest saved and years removed.

£21,930 interest saved by £100/month extra
2y 10m paid off sooner
£1,517 total monthly payment

Base payment £1,417 on £255,000 at 4.5% over 25 years. Overpaying £100 a month clears it in 22 years 2 months. Check your deal’s early repayment charge: most allow 10% a year without penalty.

Year by year
YearBalanceInterestRepaidRemaining 1 £11,334 £6,874 £248,126 2 £11,019 £7,190 £240,936 3 £10,688 £7,520 £233,416 4 £10,343 £7,866 £225,550 5 £9,981 £8,227 £217,323 6 £9,604 £8,605 £208,718 7 £9,208 £9,000 £199,718 8 £8,795 £9,414 £190,304 9 £8,362 £9,846 £180,458 10 £7,910 £10,299 £170,159 11 £7,437 £10,772 £159,388 12 £6,942 £11,267 £148,121 13 £6,424 £11,784 £136,337 14 £5,883 £12,325 £124,012 15 £5,317 £12,892 £111,120 16 £4,725 £13,484 £97,636 17 £4,105 £14,103 £83,533 18 £3,457 £14,751 £68,781 19 £2,780 £15,429 £53,352 20 £2,071 £16,138 £37,215 21 £1,329 £16,879 £20,335 22 £554 £17,655 £2,681 23 £14 £2,681 £0

Generic arithmetic, not financial advice: real offers depend on credit checks, fees, fixes and affordability rules. Product fees and rate changes after a fixed period are not modelled.

All arithmetic runs in your browser. Incomes and property figures are never transmitted.

Guide

How to use it

  1. Enter your mortgage as it stands: outstanding-ish price and deposit (or price minus deposit equal to your balance), rate and remaining term.
  2. Set the monthly overpayment you are considering.
  3. Read the headline: interest saved and time cut. The table shows the balance falling faster year by year.
  4. Before setting up the payment, check your deal’s early repayment charge, most fixes allow 10% of the balance per year penalty-free.

Examples

What overpaying buys

£100/MONTH

On the default £255,000 loan at 4.5% over 25 years, £100 extra a month saves roughly £23,000 of interest and finishes about 3 years early. The pound signs compound in your favour for once.

LUMP VS MONTHLY

A £12,000 lump sum now beats £100 a month for ten years, earlier money works longer. Model a lump by reducing the price/deposit gap and comparing.

OVERPAY VS SAVE

Overpaying "earns" your mortgage rate, tax-free and risk-free. Beat it only if savings pay more after tax, or if you lack an emergency fund, build that first, it outranks everything.

Method

How it works

The calculator runs the amortisation twice, with and without the extra payment, and reports the difference in total interest and in months to zero. Overpayments go entirely against principal, which is why their effect compounds: every pound repaid stops earning interest against you for the rest of the term.

Early repayment charges are the one catch: inside a fixed or discounted period, lenders typically cap penalty-free overpayment at 10% of the balance a year. The calculator does not model ERCs, check your offer document before committing.

FAQ

Frequently asked questions

Is overpaying always worth it?

After an emergency fund and any employer pension match, usually, it is a guaranteed, tax-free return at your mortgage rate. High-interest debts (cards, loans) should be cleared first, they cost more than the mortgage saves.

Monthly overpayments or a lump sum?

Earlier is better, so a lump now beats the same total dripped. But regular overpayments are behaviourally easier and most deals allow them freely within the 10% cap.

Will my lender reduce the payment or the term?

Ask for the term, keeping your payment the same is the whole point. Some lenders default to reducing the payment, which quietly undoes the benefit.

What is an early repayment charge?

A percentage fee (commonly 1 to 5%, stepping down through the fix) on overpayment beyond the allowance. Time big lump sums for the fix’s end if the ERC would bite.

Can I stop overpaying if money tightens?

Voluntary overpayments stop whenever you like. That flexibility is an argument for overpaying rather than shortening the contractual term at remortgage.

Does overpaying help me remortgage?

Yes, a lower balance means a lower loan-to-value band, which unlocks cheaper rates at the next deal. The saving compounds twice.

More tools

Related tools