If you’ve missed the Self Assessment registration deadline, register with HMRC straight away. HMRC doesn’t charge an automatic fine for registering late. A failure to notify penalty only applies if you also have tax unpaid after 31 January, and it’s a percentage of that unpaid tax. If you owe nothing, there’s no penalty.
It’s October, and a friend has just told you that new sole traders had to register for Self Assessment by 5 October. Your stomach drops. You started selling online last year, you’ve made a few thousand pounds, and you never told HMRC. More than 640,000 people registered for Self Assessment in the 12 months to 31 March 2026, and plenty only find out about the date after it has gone. A missed Self Assessment registration deadline feels like a big problem, but it’s usually one you can fix.
The deadline is 5 October after the end of the tax year. For the 2025 to 2026 tax year, that was 5 October 2026. It applies if you became self-employed, started renting out property or had another new source of untaxed income in that year. HMRC reported that 11.48 million people filed a Self Assessment return by the 31 January 2026 deadline for the 2024 to 2025 tax year, and 97.25% did it online. But you can’t file until HMRC has registered you and sent your Unique Taxpayer Reference (UTR), and that takes time. So, the longer you leave a missed Self Assessment registration deadline, the more it squeezes your January deadline.
In this blog, you will learn what the 5 October deadline is, what a failure to notify penalty can cost, what to do now, how to protect your 31 January deadline if your UTR is slow to arrive, and how to ask HMRC to reduce a penalty.
Is There a Penalty for Missing the Self Assessment Registration Deadline?
If you started trading at any point between 6 April 2025 and 5 April 2026, you had to register by 5 October 2026. The same date applies to new landlords, partners in a new partnership and people with other untaxed income or gains.
There’s no automatic fine because the date itself isn’t a penalty date. HMRC doesn’t charge you simply for registering late. A failure to notify penalty only comes into play when the delay leaves tax unpaid on 31 January. HMRC calls that unpaid tax “potential lost revenue”. If you pay what you owe on time, there’s nothing to base a penalty on.
So a missed Self Assessment registration deadline is something to fix quickly, not a fine waiting to land on your doormat. The real risk comes later, when a slow UTR pushes you towards a late return or a late payment.
What to Do Now: Register With HMRC Today
Don’t wait for the perfect moment for missed self assessment registration. Take these steps today:
- Check you need to register: Self employed income over £1,000 before expenses usually means yes. The same £1,000 limit applies to property income. Selling a few unwanted items online may not count as trading.
- Register Online: Search “Register for Self Assessment” on GOV.UK and pick the self employed or not self employed route. If you have a Personal Tax Account, you can register through it and see your UTR in your account within 72 hours. New customers sign in with GOV.UK One Login. Registering as self employed also sets up your National Insurance contributions.
- Note the date you registered: It’s useful proof later.
- Start gathering your records: Pull together income, expenses and bank statements while you wait for your UTR.
- Consider asking an accountant: They can register you and handle HMRC for you.
What Happens to Your 31 January Deadline if You Register Late?
Registering late doesn’t change how much tax you owe. It changes how much time you have to get ready.
Your self assessment payment deadline date stays at 31 January 2027. If HMRC issues your notice to file on or before 31 October, your online return is also due by 31 January. If the notice is issued after 31 October, the online filing deadline is three months from the date of the notice.
Your first January bill can be bigger than you expect. It can include your 2025 to 2026 balance plus a first payment on account towards 2026 to 2027. If you can’t pay in full, contact HMRC about Time to Pay before the deadline.
If you register in late October, you’d normally have both well before January. But post goes astray, so here’s how to protect yourself:
- Register as early as you can, every week counts.
- If your UTR hasn’t turned up within the stated time, call HMRC’s Self Assessment helpline on 0300 200 3310.
- Have your figures ready so you can file the day your account is live.
- Save your registration confirmation and note the date of any call to HMRC.
If a UTR delay is HMRC’s fault, that may count as a reasonable excuse. It isn’t guaranteed, which is why keeping records matters.
How Much Is a Failure to Notify Penalty?
A failure to notify penalty is what HMRC can charge when you should have told them about new income, didn’t, and some tax ended up unpaid. It’s a percentage of that unpaid tax. The rate depends on why you were late:
- Non deliberate: you didn’t know about the rule or simply forgot. The penalty can be up to 30% of the unpaid tax.
- Deliberate: you knew and chose not to register. The penalty can go up to 70%.
- Deliberate and concealed: you knew and tried to hide the income. The penalty can reach 100%.
HMRC can lower the rate if you tell them before they contact you, and if you cooperate fully. For a failure that is not deliberate, telling HMRC unprompted within 12 months can in some cases reduce the penalty to 0%. If you owe no tax, there’s no failure to notify penalty at all.
Keep this separate from late filing and late payment penalties. A late return costs £100 straight away, with more added the longer it drags on. Late payment penalties start 30 days after the due date, and HMRC also charges interest on unpaid tax.
Three late registrants, three outcomes
Here are three example cases.
| Case | Situation | Outcome |
|---|---|---|
| Maria, tutor | Earned about £9,000, registered on 14 October. | Under the personal allowance, so no tax and no penalty. She still files her return. |
| Dan, plumber | £32,000 profit, registered on 12 October, filed and paid by 31 January. | No unpaid tax, so no penalty. His income is over £30,000, so MTD for Income Tax is likely from April 2027. |
| Sam, furniture seller | About £28,000 profit, ignored registration. HMRC wrote in spring 2027 and he owes about £4,000 that was due on 31 January. | A penalty of up to 30% (£1,200) for a failure that is not deliberate, plus possible late filing and late payment penalties and interest. Telling HMRC early could reduce the rate. |
Same missed date, three very different results. What decides it is whether tax went unpaid after 31 January.
Will Making Tax Digital Affect You?
Your 2025 to 2026 return also decides whether you join MTD for Income Tax. If your gross income from self employment and property is over £30,000, you must follow MTD from 6 April 2027. The test uses income before expenses, not profit. If it applies, HMRC should write to you after you file.
Can the penalty be reduced or cancelled?
Yes, in some cases. HMRC won’t charge a penalty if you have a reasonable excuse. That could be a serious illness, a bereavement, a fire or flood at your home, or a problem with HMRC’s own systems. Not knowing about the rule usually isn’t enough on its own, but explaining your full situation is still worth doing.
If you disagree with a penalty, you generally have 30 days from the date on the penalty letter to appeal.
So don’t sit on a penalty letter. Check the date, gather your evidence and respond quickly.
How MyIVA can help
A missed Self Assessment registration deadline can feel stressful, especially when you’re also running a small business or juggling a job. MyIVA works with sole traders, individuals and small firms every day, so here’s how it can help with the issues covered above.
- Register you with HMRC: MyIVA can handle your Self Assessment registration so it’s done correctly and as soon as possible.
- Prepare and file your return: MyIVA can complete your self assessment tax return and send it to HMRC well before 31 January.
- Work out your tax bill: You’ll know what you owe and when, including any payment on account and whether MTD applies.
- Respond to HMRC about penalties: If you receive a letter, MyIVA can help you explain your situation clearly.
Missed the Self Assessment registration date?
MyIVA can register you with HMRC, prepare your return and deal with any penalty letter, so you are ready well before 31 January.
FAQs: Frequently Asked Questions
Is there an automatic fine on 6 October?
No. HMRC doesn’t charge an automatic fine for missing the registration date. A penalty only applies if you also have tax unpaid after 31 January.
Can I still register after 5 October?
Yes. You can register at any time, and you should do it as soon as you realise. The sooner you register, the sooner you get your UTR.
Is my tax still due on 31 January?
Yes. Your payment date is still 31 January, even if you registered late. If HMRC issues your notice to file after 31 October, your online filing deadline can be three months from the notice, but payment is still due on 31 January.
What if I owe no tax?
Then there’s no potential lost revenue, so there should be no failure to notify penalty. You may still need to register and file a return.
What if I forgot to register in earlier years?
Register now and tell HMRC about every year affected, then file a return for each one. HMRC can look back several years, and telling them first can lower any penalty.
Conclusion
A missed Self Assessment registration deadline sounds scary, but it isn’t an automatic fine. HMRC doesn’t charge you for being late to register. A penalty only appears when some tax is unpaid after 31 January, and even then it’s a percentage of that unpaid amount.
The best thing you can do is act quickly. Register with HMRC, keep an eye out for your UTR and get your records together. If you’ve already had a letter about a penalty, check whether you have a reasonable excuse and respond within the time limit. Acting quickly gives you the best chance of little or no penalty.
