UK Self Assessment Deadlines: A Sole Trader's Tax Calendar (2026–2027)

Three Dates Anchor the Whole System

The UK tax year runs from 6 April to the following 5 April, and Self Assessment funnels almost everything into a handful of dates. For the tax year ending 5 April 2026 (2025/26), the three dates that matter most are: register with HMRC by 5 October 2026 if you are new to Self Assessment, file your online return by 31 January 2027, and pay any tax you owe by the same 31 January 2027 deadline.

If you became self-employed during 2025/26 and have not registered yet, the 5 October 2026 deadline is the one approaching soonest. It applies to the tax year after the one in which your self-employment started, so acting now keeps you compliant before the current season accelerates.

Filing Your 2025/26 Return

Most sole traders file online, and the online deadline for the 2025/26 return is midnight on 31 January 2027. If you insist on a paper return, it must arrive by 31 October 2026—three months earlier. Filing on time matters: a late return triggers an automatic £100 penalty even if you owe no tax, with further penalties and daily charges for longer delays.

Before you file, gather your income records, deductible business expenses and any payments on account you have already made. A quick way to sanity-check your numbers is to run your profit through a self-employment tax estimator before HMRC's own calculation lands.

Class 4 National Insurance and Income Tax in 2026/27

For the 2026/27 tax year, sole traders pay Class 4 National Insurance at 6% on profits between £12,570 and £50,270 and 2% above that. Class 2 National Insurance is no longer collected for most self-employed people. Income tax uses the personal allowance of £12,570, a 20% basic rate up to £50,270, 40% up to £125,140 and 45% above—figures frozen from the previous year at the time of writing.

These are the same structures our Contractor Tax Estimator models when you switch its region to the UK: Class 4 NI plus income tax on your profit, with your personal allowance applied automatically.

Payments on Account: Tax Paid in Advance

If your 2025/26 tax and Class 4 National Insurance bill is more than £1,000 and less than 80% of it was collected through your tax code, HMRC asks you to pay your 2026/27 tax in advance. Two payments on account are due: 31 January 2027 and 31 July 2027, each equal to 50% of your previous year's bill, with any balancing payment following on 31 January 2028.

Payments on account are why your first big self-employed tax year can feel like paying double: you are settling last year's bill while prepaying half of this year's. Budget for both dates, not just January. If your income has fallen, you can ask HMRC to reduce your payments on account.

Making Tax Digital for Income Tax Is Arriving

Sole traders and landlords with qualifying income above £50,000 move to Making Tax Digital (MTD) for income tax from April 2026, keeping digital records and sending quarterly updates to HMRC instead of a single annual declaration. Businesses with income above £30,000 join from April 2027, with the regime phasing in for others afterwards. The exact thresholds and dates are confirmed on GOV.UK, so check your position before the start of the tax year that applies to you.

Your 2026–2027 Checklist

Register with HMRC by 5 October 2026 if you are new. Keep complete digital records of income and expenses through the year. Estimate your tax before filing so there are no surprises, then file online and pay what you owe by 31 January 2027. Mark 31 July 2027 for the second payment on account. Run your numbers through the estimator below to see your Class 4 NI, income tax and net profit for the current year.