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.
Know what 31 January costs you - long before 31 January
A deadline only hurts when the number behind it is a surprise. Invoice through this site and your income tax and National Insurance estimate updates as you get paid, on the same HMRC rates as the calculator here. It is an estimate before expenses, and before any payments on account HMRC asks you for.
- Send a clean, numbered invoice in about a minute - VAT handled per line if you are registered, PDF at the end.
- A live set-aside figure for the tax on what you have actually been paid, so the balancing payment is money you have already put by.
- Every invoice, payment and due date in one place when the return is due.
No password and no card. Enter your email, click the link we send, and you are in.
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.