Self Assessment 2026/27: Deadlines, Making Tax Digital and the Dates That Matter

If you're self-employed, a landlord, a company director with untaxed income, or you earn on the side, Self Assessment is how you tell HMRC what you owe. Miss a date and the penalties start automatically - get organised early and it's genuinely painless. Here's everything that matters this year, in plain English.

The deadlines to put in your diary now

·      5 October 2026 - if you've never filed before and had taxable income in 2025/26, you must register with HMRC by this date.

·      31 October 2026 - deadline for paper returns for the 2025/26 tax year.

·      31 January 2027 - deadline for online returns and for paying your bill. This is the big one: file late and a £100 penalty applies immediately, even if you owe nothing.

·      31 July 2027 - second payment on account, if payments on account apply to you.

Our advice every single year: don't wait for January. Filing early doesn't mean paying early - you still have until 31 January to pay - but it means you know the number months in advance and can plan for it.

Payments on account: the bill that surprises people

If your tax bill is more than £1,000, HMRC usually asks you to pay next year's tax in advance, in two instalments (31 January and 31 July), each half of this year's bill. In your first year this feels like paying one-and-a-half years of tax at once - it isn't, but it does hit cashflow. If you know your income is falling, we can apply to reduce them so you aren't lending HMRC money.

Making Tax Digital: the biggest change to Self Assessment in a generation

Making Tax Digital for Income Tax is now live. From April 2026, sole traders and landlords with combined qualifying income over £50,000 (broadly, gross self-employment plus property income before expenses) must keep digital records and send HMRC quarterly updates through compatible software - the first quarterly updates are due in August 2026. The threshold drops to £30,000 from April 2027 and £20,000 from April 2028, so most self-employed people will be inside the system within two years.

If that sounds like four deadlines instead of one - you're right, and that's exactly why our clients hand it to us. We set up the software, connect your records and handle every quarterly submission. Personal Tax Service

Don't leave money on the table: expenses and allowances

Most people overpay because they under-claim. The rule: costs incurred wholly and exclusively for your business are deductible. For 2026/27 that includes the flat-rate mileage allowance - now 55p per mile for the first 10,000 business miles (it was 45p for years, so old guides are wrong) - home-working flat rates, and pre-trading costs from up to 7 years before you started. If your side income is small, the £1,000 trading allowance may mean you owe nothing at all. Read our full guide.

And keep your records - HMRC requires them for at least 5 years after the 31 January deadline.

Want a quick estimate right now?

Try our free self-employed tax calculator - enter your profit and see your Income Tax and National Insurance for 2026/27 in seconds.

Frequently asked questions

When is the Self Assessment deadline for the 2025/26 tax year? Online returns and payment are due by 31 January 2027. Paper returns are due earlier, by 31 October 2026. If you have never filed before, you must register with HMRC by 5 October 2026.

Who has to use Making Tax Digital for Income Tax? From April 2026, sole traders and landlords with combined qualifying income over £50,000 must keep digital records and send quarterly updates to HMRC through compatible software. The threshold drops to £30,000 from April 2027 and £20,000 from April 2028.

What are payments on account? If your Self Assessment bill is over £1,000, HMRC usually asks you to pay next year's tax in two advance instalments - 31 January and 31 July - each half of this year's bill. Many people are caught out by the first one, which lands on top of the current year's bill.

How long do I need to keep my records? If you are self-employed, HMRC requires you to keep your records for at least 5 years after the 31 January submission deadline of the relevant tax year.

If you're self-employed, our accountants for sole traders can handle registration and filing for you.

Not sure what you can claim? See our guide to sole trader expenses.

Or let us do the whole thing - see our personal tax return service