Self Assessment deadlines and penalties: key dates every UK taxpayer must know
Summary
Updated April 2026 — Sources: GOV.UK Self Assessment deadlines, HMRC SAM140000.
Missing Self Assessment deadlines triggers automatic penalties and interest. Every UK sole trader, landlord, and company director with untaxed income must know these dates.
1. Key deadlines for 2025/26
| Action | Deadline |
|---|---|
| Register for Self Assessment | 5 October 2026 |
| File paper return | 31 October 2026 |
| File online return | 31 January 2027 |
| Pay tax owed | 31 January 2027 |
| First payment on account | 31 January 2027 |
| Second payment on account | 31 July 2026 |
2. Late filing penalty structure
- 1 day late: £100 (even if no tax due)
- 3 months late: £10/day for 90 days (max £900)
- 6 months late: £300 or 5% of tax due (whichever is higher)
- 12 months late: another £300 or 5% of tax due
3. Late payment charges
Interest accrues daily on unpaid tax from the due date. A 5% surcharge applies at 30 days, 6 months, and 12 months after the deadline. Budget payments on account to avoid January cashflow shocks.
4. How to avoid penalties
- Set calendar reminders for all key dates
- Submit your return even if you cannot pay — filing and paying are separate obligations
- Contact HMRC to arrange Time to Pay if struggling
- Keep digital records throughout the year (MTD-ready)
5. Sources
FAQ
When is the Self Assessment filing deadline?
31 January following the end of the tax year (which runs 6 April to 5 April). For 2025/26 income, file by 31 January 2027. Online filing is mandatory for most taxpayers.
What is the late filing penalty?
£100 fixed penalty if one day late. After 3 months: £10/day for up to 90 days. After 6 months: greater of £300 or 5% of tax due. Penalties escalate further after 12 months.
When are tax payments due?
Balancing payment and first payment on account: 31 January. Second payment on account: 31 July. Payments on account apply when your previous year tax bill exceeded £1,000.