The key dates at a glance
5 October 2026 is the deadline to tell HMRC you need to file a Self Assessment return for the 2025/26 tax year, if you have not filed before. 31 October 2026 is the deadline for filing that return on paper, and 31 January 2027 is the online filing deadline, along with the deadline to pay the tax you owe for 2025/26 and your first payment on account, if payments on account apply to you.
If you are registered for Making Tax Digital for Income Tax, different quarterly update deadlines apply instead. Check which regime applies to you before you plan your year.
If you miss a deadline
Late filing penalties start from £100 and grow the longer a return is outstanding, with daily penalties after three months and percentage-based penalties after six. Late payment attracts interest as well as penalties. If you have a genuine reason for a delay, you can appeal, and HMRC may apply a reasonable excuse.
The cheapest penalty is the one you never incur: file on time even if you cannot pay in full, then agree a payment plan with HMRC. Filing on time and paying late is always better than doing neither.
Make the dates work for you
Rather than treating 31 January as an annual emergency, spread the work. Keeping income and expenses up to date through the year means January is a review, not a scramble. Set your own internal deadline a few weeks early so there is room to fix anything unexpected.
MyTaxFiling tracks what you have recorded and what is still outstanding through the year, so the deadline takes care of itself.