The 5 October deadline has passed. If you needed to register for Self Assessment for the first time for the 2025/26 tax year and didn’t, don’t panic. You can still fix it, but you should act today.
Here is what missing the deadline means, how to register late, and which penalties you may face.
What Missing 5 October Actually Means
You had to tell HMRC by 5 October 2026 if you needed to complete a tax return for 2025/26 and you had never filed one before. The same deadline applied if you registered before but did not need to send a return for 2024/25.
Missing the registration deadline does not automatically bring the £100 late-filing fine. That fine applies when a required tax return goes in late, not when registration goes in late.
But you are not off the hook. HMRC can charge a “failure to notify” penalty when you tell them late. The sooner you register, the smaller the risk.
Step 1: Check Whether You Need to File at All
Before you register, make sure you actually need to. HMRC’s free online checker on GOV.UK takes a few minutes and tells you whether you must send a Self Assessment return.
You typically need to register if, between 6 April 2025 and 5 April 2026, you:
- Became self-employed with gross trading income over £1,000
- Started a business partnership
- Earned untaxed income over £2,500
- Had income over £100,000, or kept Child Benefit while earning over £60,000
If you registered for Self Assessment before but skipped the 2024/25 return, you may need to reactivate your existing account rather than start a fresh registration. Check for your old Unique Taxpayer Reference (UTR) before you begin.
Step 2: Register Right Now
Register through GOV.UK as soon as you finish reading this. HMRC’s new digital registration service issues your UTR in your Personal Tax Account within 72 hours much faster than the old 15-day postal wait.
Do not wait for HMRC to contact you first. Coming forward yourself matters: HMRC treats unprompted disclosure much more kindly when it sets penalties.
Step 3: Know Your New Deadlines
When you register after 5 October, HMRC sends you a letter or email with a new deadline for your tax return. You normally get three months from the date on that letter or email.
One deadline does not move: you must still pay any tax you owe for 2025/26 by 11:59pm on 31 January 2027. Miss that and penalties apply regardless of when you registered.
Planning to file on paper? The Self Assessment paper deadline is 31 October.
What Penalties Can Still Follow
Three penalty regimes can bite, in order:
1. Failure-to-notify penalty. This is the one tied to late registration. It is a percentage of the tax you failed to notify, not a fixed fine:
- Not deliberate, and you come forward yourself: 0% to 30%
- Deliberate but not concealed: 20% to 70%
- Deliberate and concealed: 30% to 100%
- A genuine reasonable excuse (serious illness, for example): no penalty
2. Late-filing penalties. If you miss the return deadline HMRC sets for you: £100 straight away, then £10 a day after three months (up to £900), then 5% of the tax due or £300, whichever is greater, at six months, and again at twelve months.
3. Late-payment penalties. Miss 31 January 2027 and HMRC charges 5% of the unpaid tax at 30 days, again at six months, and again at twelve months, plus interest from day one.
The pattern is simple: register now, file on time, pay on time.
Start Keeping Records Today
If you are newly self-employed, you also need to know about Making Tax Digital. From April 2026, self-employed people and landlords with qualifying income over £50,000 must keep digital records and send quarterly updates through compatible software.
iFiler is HMRC-recognised software for MTD Income Tax quarterly updates. It keeps your income and expense records organised through the year, so your figures are ready when filing time comes. It is free for now.
Frequently Asked Questions
No. Register as soon as you can through GOV.UK. HMRC will then give you a new deadline, usually three months from the date of its letter or email, to send your return.
No. The £100 late-filing fine applies to a tax return filed late, not to late registration. You may face a failure-to-notify penalty instead, which is a percentage of the tax involved.
HMRC’s digital service puts your UTR in your Personal Tax Account within 72 hours. The old postal route could take up to 15 days.
Yes. If the failure was not deliberate and you disclose it without being prompted, the failure-to-notify penalty can be reduced to 0%. Waiting for HMRC to find you removes that benefit.
31 January 2027. Whatever your registration history, you must file your online return and pay your 2025/26 tax bill by 11:59pm that day.
If HMRC sends you a tax bill instead of asking you to file a return, read our guide to Simple Assessment letters and how to avoid paying twice.
Disclaimer:
This guide provides general information about Self Assessment as of October 2026. Tax rules and HMRC guidance can change. Always consult with a qualified tax professional about your specific circumstances. That’s what we’re here for. In accordance with our normal practice this reference is given in good faith and in confidence, without legal liability on the part of the author or the company. The author assumes no responsibility or liability for any errors or omissions in the content of this site
The information provided in this blog is for general guidance and educational purposes only and does not constitute financial, tax, accounting or legal advice. iFiler, registered in England under Company Registration Number 15996173, has prepared this content to offer general insights into financial and taxation matters. Although every effort is made to ensure the accuracy and relevance of the information at the time of publication, no guarantee is given regarding completeness, accuracy or suitability for your specific circumstances.
Readers should not act, or refrain from acting, based solely on the information contained in this content. Professional advice tailored to your personal or business situation should always be obtained before taking any financial or tax related decision. iFiler accepts no liability for any loss or damage arising from reliance on the information presented in this blog.
