Self Assessment Tax Calculator 2025/26

Your Self Assessment bill for 2025/26 is due on 31 January 2027, and for most sole traders and landlords it isn't the only thing due that day. HMRC also asks for the first of two payments on account towards 2026/27, each worth half of your 2025/26 bill. The second follows on 31 July 2027. So the amount you pay in January is: your 2025/26 tax, minus what you already paid on account for it in January and July 2026, plus half of your 2025/26 bill. This calculator works out each figure from your income, using the 2025/26 rates on GOV.UK: income tax, Class 4 National Insurance, and the 20% tax reduction landlords get on mortgage interest. It also tells you whether your 2025/26 turnover brings you into Making Tax Digital from April 2027.

Scenario: started trading in 2025/26, turnover £45,000, expenses £5,000, so a profit of £40,000. No other income and no payments on account made yet.

The 2025/26 bill: - Income tax: 20% × (£40,000 − £12,570) = £5,486.00 - Class 4 NI: 6% × (£40,000 − £12,570) = £1,645.80 - Total: £7,131.80

What's due: - 31 January 2027: £7,131.80 balance + £3,565.90 first payment on account = £10,697.70 - 31 July 2027: second payment on account = £3,565.90

That's 150% of the year's tax in January, which is why a first Self Assessment bill catches so many people out. From the second year, the payments on account already made come off the January balance. Turnover of £45,000 is over £30,000, so this sole trader also needs Making Tax Digital from 6 April 2027.

HMRC only asks for payments on account if your Self Assessment bill is £1,000 or more. They also don't apply if more than 80% of your tax was already paid outside Self Assessment, which is common when most of your income is a salary taxed through PAYE.

If you expect 2026/27 to be lower, for example because you stopped trading or sold a rental property, you can reduce them in your HMRC online account or with form SA303. Reduce them too far and HMRC charges interest on the shortfall.

For homes you let, you can't deduct mortgage interest from rent. Instead you get a tax reduction of 20% of the lowest of: your finance costs, your property profits, and your income above the personal allowance. A higher-rate landlord gets 20% back on interest, not 40%.

For example, a landlord with a £30,000 salary, £20,000 rent, £2,000 of expenses and £8,000 of mortgage interest has a property profit of £18,000 and a £1,600 tax reduction. Any finance costs that don't get relief carry forward to the next year.

The 2025/26 return decides who joins Making Tax Digital for Income Tax in April 2027. HMRC adds your turnover from self-employment and property, before expenses. If it's more than £30,000, you'll need compatible software and quarterly updates from 6 April 2027. Over £20,000 on the 2026/27 return brings you in from April 2028. Salary, dividends, pensions and partnership profits don't count. Check the details with the MTD compliance checker.

Speak to an accountant if you have losses to set against other income, a partnership, foreign income, capital gains, large pension contributions, or you're a Scottish taxpayer. This calculator covers employment, self-employment and UK property income at 2025/26 rates for England, Wales and Northern Ireland. It doesn't include savings, dividends, capital gains, student loans, Gift Aid or the £1,000 trading and property allowances.