Mortgage overpayments

A mortgage is one of the biggest costs you’ll ever carry — and overpaying it is one of the most reliable ways to shrink that cost. Because interest is charged on the outstanding balance, every extra pound you pay cuts the amount the bank earns from you, month after month, for the rest of the term.

Why it works

Interest is calculated on your remaining balance. The standard payment clears the loan over the full term, but an overpayment comes straight off the principal. That means:

• you pay interest on a smaller balance each month
• the loan clears early — often years early
• the total interest you pay falls substantially

Example. A £150,000 mortgage at 4% over 25 years costs about £792 a month. Add £200 a month and the loan clears around five years early — saving tens of thousands in interest. The exact figure depends on your rate and term, and the overpayment calculator shows it precisely.

Overpaying vs saving

The natural question: should overpayments go into a savings account instead? Compare the rates:

• Mortgage interest — usually 4%+ and effectively tax-free because it’s interest you don’t pay
• Savings interest — often lower, and taxed above your Personal Savings Allowance

Unless you need the cash at short notice, overpaying generally wins. The exceptions are clear: build an emergency fund first, and clear higher-interest debts (credit cards, loans) before the mortgage.

The 10% rule

Most lenders let you overpay up to 10% of the balance per year without a penalty. Above that, early repayment charges typically apply. A common strategy is to set up a monthly overpayment within the limit, then add a lump sum (bonus, tax refund) if you’re still under the annual allowance.

The flexibility trap

Overpayments are usually locked in — you can’t easily pull the money back out if circumstances change. So a sensible order is:

1. Emergency fund in easy-access cash first
2. Pension contributions up to your employer match
3. Then overpay the mortgage

Once those two bases are covered, overpaying is one of the safest, most tax-efficient uses of spare cash you’ll find.

See the maths

Use the mortgage overpayment calculator to see your exact interest saving and new pay-off date, the mortgage calculator for the standard payment, and the savings calculator to compare overpaying against saving the same amount.