Should I Overpay My Mortgage or Save? A UK Decision Guide

Got spare cash each month? You can put it towards your mortgage or into savings. Both are sensible, but which is better depends on interest rates, tax and how much you value flexibility.

The core comparison

Overpaying earns you a return equal to your mortgage rate. Every £1 you overpay saves the interest you’d otherwise have paid on it. That return is guaranteed and tax-free.

Saving earns the account’s interest rate, which may be taxed outside an ISA. Your money stays accessible.

So, roughly:

• if your mortgage rate is higher than what you can earn tax-free, overpaying wins on pure numbers;
• if you can earn more in savings, after tax, saving wins and keeps your options open.

A worked example

On a £200,000 mortgage at 4.5% over 25 years, overpaying £200 a month saves £36,281 of interest and clears the mortgage 6 years and 1 months early.

Saving the same £200 a month in an ISA at 4.5% for 10 years builds £30,095, including £6,095 of interest. When the rates are equal, the outcomes are similar. The difference is access: the savings are yours to use, while overpayments are locked in the house.

Questions to ask first

1. Do I have an emergency fund? Keep 3–6 months of essential spending in easy-access savings before overpaying. Money in your mortgage is hard to get back out.
2. Do I have more expensive debt? Credit cards, overdrafts and car finance usually cost more than your mortgage. Pay those first. See the debt payoff planner.
3. Am I getting my full employer pension match? Extra pension contributions often come with employer money and tax relief, which beats almost anything else.
4. Is my mortgage rate fixed and low? If you fixed at 1.5–2.5%, savings at 4%+ beat overpaying for now.
5. Will I remortgage soon? A lump sum just before a remortgage can drop you into a cheaper LTV band. That’s a big bonus.

Tax makes a difference

Savings interest outside an ISA is taxed above your Personal Savings Allowance (£1,000 for basic-rate, £500 for higher-rate, £0 for additional-rate taxpayers). For a higher-rate taxpayer, a 4.5% savings rate taxed at 40% is only 2.7% after tax. Overpaying a 4.5% mortgage wins easily. From April 2027 savings income tax rates rise by 2 points.

Flexibility: a middle path

• Save first, overpay later. Build savings in an ISA, then make a lump-sum overpayment before your fix ends or when you remortgage.
• Offset mortgage. Savings in a linked account reduce the interest you pay, but stay accessible.
• Check your ERC allowance. Most fixed deals let you overpay up to 10% a year. Plan larger amounts around your deal end date.

Run your numbers

Compare the mortgage overpayment calculator with the savings calculator using your actual mortgage rate and the best savings rate you can get. Each one passes values to the other, so you can switch between them with one click.