Tools / Overpay or save calculator
Overpay or save calculator

Overpay the mortgage, or put the money somewhere else?

Compare overpaying with a savings account, an ISA, a general investment account and your pension. Each one is worked out after UK tax, using the rules for 2026/27 and the changes already announced.

Your mortgage

Use today's balance and rate, and the time left on the mortgage.

£
%
years
Your spare money
£
£
Your tax
£
Salary plus any other taxable income, before pension contributions.

That's the personal savings allowance, the £500 dividend allowance and the £3,000 capital gains allowance.

Where else it could go
Savings account
%
ISA
%
A cash ISA's interest rate, or what you expect a stocks and shares ISA to grow by after fees.
General investment account
%
%
Pension
%
£ a month
Only what they'd add because you pay more in, like a matched contribution.
Show results

Before you choose

  • Build that first, in easy-access savings. Overpaid money is hard to get back, and investments can be down when you need them.

  • Clear credit cards, overdrafts, car finance and personal loans first. They almost always cost more than any option here earns.

  • If paying a bit more in would get your employer to add more, do that first. Add what they'd put in under Pension to see the difference.

The answer

Overpay the mortgage
Savings account
Tax
Rate to break even
ISA
Tax
Rate to break even
General investment account
Tax
Growth to break even
Pension
Tax relief added
Tax when you take it
Growth to break even

What your money is worth over time

After tax, if you cashed it in that month. For overpaying, it's how much less you owe.

  • Overpay the mortgage

Year by year

What each option is worth after tax at the end of each year

Year Overpay Savings ISA GIA Pension

What the numbers don't show

  • Overpaying is a guaranteed return. Investments in an ISA, GIA or pension can fall, and the rates above are your guesses.
  • Money you overpay is locked into your home. You can't easily get it back without remortgaging, so keep an emergency fund first.
  • Your mortgage rate will change when your deal ends. A higher rate makes overpaying more valuable.
  • Employer pension contributions are only included if you enter them under Pension. Free money from your employer usually beats everything else.
  • Most fixed-rate deals cap overpayments at 10% of the balance a year. Check your early repayment charges.

These figures are an illustration, not financial advice. We assume your mortgage rate, the growth rates and your tax band stay the same, and that pots are cashed in on the date shown. Tax uses 2026/27 rules and changes already announced: savings tax rises by 2 points from April 2027, and the National Insurance saving on salary sacrifice is capped at £2,000 a year from April 2029. We don't model the starting rate for savings or spreading capital gains over several years. Pension relief is worked out from your income, including the personal allowance taper between £100,000 and £125,140, and any relief above the basic rate is assumed to be claimed and paid into the pension. Tax thresholds are assumed to stay frozen.