Self-Assessment Deadlines 2026/27: When to File and When to Pay

The main self-assessment deadline is 31 January following the end of the tax year, by which date you must file your online tax return and pay any tax you owe. For the 2025/26 tax year, that filing and payment date is 31 January 2027. A clear self-assessment tax return guide matters because the dates are unforgiving: HMRC charges an automatic £100 penalty the moment an online return is late, even if no tax is due. Blue Tick Accountants, a Guildford-based UK tax advisory and accountancy practice, helps self-employed people across the UK meet every deadline and pay the right amount on time. This guide sets out the key self-assessment dates for 2026/27, how payments on account work, the penalties for missing a deadline, and how Making Tax Digital changes the picture.

Key Takeaways

• The online self-assessment deadline is 31 January following the tax year end, so the 2025/26 return must be filed by 31 January 2027.
• The deadline to register for self-assessment is 5 October following the end of the tax year in which you started trading, and paper returns are due by 31 October.
• Any balancing payment of tax is due by 31 January, with payments on account due by 31 January and 31 July.
• Missing the filing deadline triggers an automatic £100 penalty, even when no tax is owed, with daily penalties of £10 building after three months.
• Under Making Tax Digital for Income Tax, sole traders and landlords with qualifying income above £50,000 must, from 6 April 2026, keep digital records and submit quarterly updates plus a final declaration by 31 January.

What Are the Key Self-Assessment Dates for 2026/27?

The self-assessment year runs to 5 April, and the deadlines that follow are fixed dates. For income earned in the 2025/26 tax year, which ended on 5 April 2026, four dates matter: register by 5 October 2026 if you became self-employed during 2025/26 and have not filed before; file a paper return by 31 October 2026; file online by 31 January 2027; and pay any tax owed for 2025/26 by that same 31 January 2027 date.

For a complete walkthrough of how to complete the return, including the pages, income sources, and allowable expenses, see our guide to self-assessment tax returns.

How Do Payments on Account Work?

Payments on account are advance instalments towards your next tax bill, due in two equal halves on 31 January and 31 July. HMRC requires them once your self-assessment tax bill exceeds £1,000, and each instalment is 50% of the previous year's tax. The system catches many people out in their second year of trading, because the 31 January payment can include both the balancing payment for the year just gone and the first payment on account for the year ahead.

Worked example. A sole trader owes £4,000 in tax for 2025/26. On 31 January 2027 they pay the £4,000 balancing payment plus a first payment on account of £2,000, a total of £6,000, then a second £2,000 instalment on 31 July 2027. These instalments are credited against the eventual 2026/27 bill, so they are not extra tax, but they do bring the cash payment forward.

What Are the Penalties for Filing or Paying Late?

Late filing and late payment carry separate penalties, so a return that is both filed and paid late attracts both, and the filing penalty applies even when no tax is due.

Filing an online return after 31 January triggers an immediate £100 penalty. After three months, daily penalties of £10 apply for up to 90 days, a maximum of £900. At six months a further penalty of 5% of the tax due or £300, whichever is greater, applies, with the same again at twelve months. Late payment penalties are charged at 5% of the unpaid tax at 30 days, six months, and twelve months, and HMRC charges interest on the outstanding amount from the due date.

Worked example. A self-employed individual owes £4,000 and files their 2025/26 return six months late, paying at the same time. They face the £100 fixed penalty, £900 in daily penalties, a six-month filing penalty of £300 (the greater of 5% of the tax and £300), and late payment penalties of £200 at 30 days and a further £200 at six months, totalling £1,700 in penalties, plus interest, before they have settled the original £4,000.

How Does Making Tax Digital Change Self-Assessment Deadlines?

Making Tax Digital for Income Tax (MTD for IT) is now live, though the 31 January final deadline remains. From 6 April 2026, anyone with qualifying income above £50,000 must keep digital records and submit quarterly updates to HMRC through compatible software, followed by a final declaration by 31 January.

Those with qualifying income above £30,000 join from April 2027, and those above £20,000 from April 2028. If your self-employed income is below £50,000 for now, you continue to file a single annual self-assessment tax return until your turnover brings you into scope. Anyone already over £50,000 should be keeping digital records for the current 2026/27 year and preparing for quarterly submissions.

Class 2 and Class 4 contributions are collected through the same return and the same January deadline, as our guide to National Insurance for the self-employed explains.

Frequently Asked Questions

When is the self-assessment deadline for 2025/26?

The online self-assessment deadline for the 2025/26 tax year is 31 January 2027, and any tax owed must be paid by the same date. If you file a paper return instead, the earlier deadline of 31 October 2026 applies. Registration for self-assessment, if you have not filed before, is due by 5 October 2026.

Do I get penalised if I file late but owe no tax?

Yes. HMRC charges an automatic £100 penalty for an online return filed after 31 January, even if you owe no tax or are due a refund. The penalty stands regardless of your tax position, and daily penalties of £10 begin once the return is three months late, so filing on time always matters.

What are payments on account?

Payments on account are two advance instalments towards your next year's tax bill, due on 31 January and 31 July, each equal to half of your previous year's tax. They are required once your tax bill exceeds £1,000. The instalments are credited against your final bill, so they reduce what you owe at the next balancing payment.

Does Making Tax Digital change when I file?

Making Tax Digital for Income Tax keeps the 31 January final deadline but adds quarterly updates for those in scope. From 6 April 2026, sole traders and landlords with qualifying income above £50,000 must submit quarterly updates through compatible software and a final declaration by 31 January, rather than a single annual return.

How Blue Tick Can Help

Blue Tick Accountants prepares and files self-assessment tax returns for sole traders and landlords across the UK, calculating your payments on account, claiming every allowable expense, and making sure you never miss the 31 January deadline. The practice also helps higher earners move smoothly onto Making Tax Digital with the right software and quarterly process. Head to our website and book a meeting now.

Conclusion

The self-assessment calendar turns on a handful of fixed dates: register by 5 October, file online by 31 January, and pay by 31 January, with payments on account falling on 31 January and 31 July. Missing any of these triggers automatic penalties that grow over time. Diarise your deadlines early, set money aside for payments on account, and if your income exceeds £50,000 prepare now for Making Tax Digital reporting.

About the Author

This guide was written by Leon, founder of Blue Tick Accountants, a Guildford-based UK tax advisory and accountancy practice that helps the self-employed, landlords, and limited company owners across the UK. It was last reviewed for the 2026/27 tax year.

This article is intended for general informational purposes only and does not constitute tax, legal, or financial advice. Tax rules are subject to change and their application will depend on your individual circumstances. You should always seek advice from a qualified professional before taking action. Blue Tick Accountants accepts no liability for decisions made on the basis of this content.

Related reading: The Most Common Self-Assessment Mistakes HMRC Sees Every Year.

Related reading: What Happens If You Miss the Self-Assessment Deadline?.