Missing a self-assessment deadline incurs automatic penalties. Here are the key dates for the 2025/26 tax year.
Key dates
- 5 April 2026: end of 2025/26 tax year
- 5 October 2026: deadline to register for self-assessment if newly self-employed
- 31 October 2026: paper return deadline for 2025/26
- 31 January 2027: online return deadline for 2025/26
- 31 January 2027: payment deadline for any tax owed
- 31 July 2027: second payment on account (if applicable)
Penalties
£100 for filing up to 3 months late. £10/day (max £900) for 3–6 months late. A further penalty of 5% of tax owed or £300 (whichever is greater) at 6 months and 12 months.
Prepare with our free self-assessment checklist.