Self Assessment deadlines (2026/27)
Every Self Assessment deadline that lands during the 2026/27 tax year, and the penalties for missing each.
Overview
Two tax years run concurrently in your accounting calendar: the year you're currently earning in, and the year you're filing the return for. The table below covers every Self Assessment date that falls between 6 April 2026 and 5 April 2027.
Quick reference: a fuller, worked-example version of this guide is in development. The figures below are accurate for 2026/27 as of the last build.
Key facts
| Tax year 2025/26 paper return | 31 October 2026 |
|---|---|
| Tax year 2025/26 online return + balancing payment | 31 January 2027 |
| Tax year 2025/26 first payment on account | 31 January 2027 |
| Tax year 2025/26 second payment on account | 31 July 2027 |
| Tax year 2026/27 register if new | 5 October 2027 |
| Tax year 2026/27 paper return | 31 October 2027 |
| Tax year 2026/27 online return | 31 January 2028 |
Penalties when you miss the 31 January online deadline
- 1 day late: £100 fixed penalty, even if you owe no tax.
- 3 months late: £10 a day for up to 90 days (max £900) on top of the £100.
- 6 months late: a further £300 or 5% of the tax due, whichever is higher.
- 12 months late: another £300 or 5% - and HMRC may add a "deliberate" surcharge on top if they think you held back information.
Late payment attracts separate penalties: 5% of unpaid tax at 30 days late, then again at 6 months and 12 months. Interest accrues daily from 1 February.
When to register
If you became self-employed during 2026/27, you must register for Self Assessment by 5 October 2027 - five months after the tax year ends. Register online via gov.uk; you'll receive a UTR (Unique Taxpayer Reference) by post within about two weeks. You'll need it to file the return.
If you've filed before, you don't need to re-register; the same UTR carries forward.
Reasonable excuses
HMRC can cancel a late-filing penalty if you have a "reasonable excuse" - typically serious illness, a bereavement, or a fire/flood that destroyed your records. Forgetting, leaving it to your accountant, or not understanding the system don't count. Appeal within 30 days of the penalty notice.
Sources
Related guides
- Class 2 and Class 4 National Insurance - full rates, thresholds and payment dates.
- Sole trader vs limited company - which structure pays less UK tax, with worked examples at £30k, £50k and £80k profit.
- Reduce your tax bill legally - the HMRC-approved levers, ordered by how much they actually move the bill.
- Allowable expenses - The HMRC-accepted categories you can deduct from profit, plus the simplified-expenses shortcut.
- Payments on account - HMRC's advance-tax mechanism explained, with the January and July payment cycle.
Or run the numbers for your own profit level: £50,000 self-employed, £75,000 self-employed, or browse all bracket pages.