31/08/2026
In the UK, the deadline to register for self-assessment is the 5th October following the end of the tax year in which you first needed to file a tax return. For example, if you first need to file a tax return for the 2025–26 tax year (which ended on 5 April 2026), you must register with HMRC by 5 October 2026. After registering, the key deadlines are:
• 31 October 2026 – paper tax return deadline.
• 31 January 2027 – online tax return deadline and payment deadline for any tax due.