31st January 2026
In the UK, if you need to complete a Self-Assessment tax return for the tax year 6 April 2024 - 5 April 2025, the key deadline you need to know right now is midnight today - 31st January 2026.
Submit your online Self-Assessment tax return by 11:59 pm on 31 January 2026 — this is the final day to file online and avoid an automatic late-filing penalty.
Here's a quick breakdown of the deadlines for this tax year:
Important Self Assessment Deadlines (UK)
31 January 2026 - Last day to submit your online tax return and pay any tax you owe without penalty.
31 October 2025 - Deadline to send a paper tax return (this has now passed).
5 October 2025 - Deadline to register for Self Assessment if it's your first time (also passed for this year).
After 31 January, late-filing penalties start immediately — usually an automatic £100 fine, with further fines and interest increasing the longer you delay.
So today (end of January 2026) is the last day to complete your return for the tax year that ended on 5 April 2025 without facing penalties.
HMRC has opened its phone help lines for an extra day today 31 January 2026 as its a Saturday.
More than 10 million people have already filed their Self-Assessment tax return with HM Revenue & Customs (HMRC) ahead of the January 31 deadline.
BUT - over 2 million people may still have to do it today to avoid penalties.
Not everyone has to submit a return but HMRC has emphasised this year that anyone with side hustles should check the guidelines.
Penalties for Filing Your Tax Return Late
Even if you don't owe any tax, HMRC will charge automatic penalties when you miss the filing deadline. These escalate the longer the return is late:
Immediate penalty (day 1+)
£100 fixed penalty as soon as your tax return is late — even if you owe nothing or have paid your tax on time.
After 3 months
£10 per day for each day your return remains outstanding.
Maximum additional penalty: £900.
After 6 months
£300 or 5 % of the tax due, whichever is higher.
After 12 months
Another £300 or 5 % of the tax due, whichever is higher.
If you leave your return more than a year late, these penalties stack up, meaning the total cost can easily run into hundreds or even thousands of pounds.
Penalties and Interest for Paying Your Tax Late
Filing your return late is one thing — paying the tax you owe late brings separate penalties and interest charges:
Late payment penalties
If you don't pay the tax due by 31 January:
30 days late: 5 % of the unpaid tax.
6 months late: another 5 % of the unpaid tax.
12 months late: an additional 5 % of the unpaid tax.
Interest charges
HMRC charges interest on any unpaid tax from the day after the deadline until it's paid in full.
Interest is charged daily and is linked to the Bank of England base rate plus a set margin — so the longer you delay, the more it accrues.
What If You Can’t Pay?
If you genuinely can’t afford to pay what you owe by 31 January, you can contact HMRC and arrange a Time to Pay plan. This lets you spread payments over several months or more, and can reduce the stress and extra costs — but you must still file on time to avoid the initial penalties.
Reasonable Excuse or Appeal
HMRC may waive penalties if you have a reasonable excuse (for example, serious illness or unexpected events), but the bar is high and you usually need evidence.
Missing the deadline can cost far more than a simple £100 fine if you delay filing or paying for months — so it’s better to file even if you can’t quite pay, then sort payment terms with HMRC.