Written for the 2025/26 tax year, the return due by 31 January 2027. Checked against GOV.UK on 6 October 2026.
If you needed to register for Self Assessment for the 2025/26 tax year and did not tell HMRC by 5 October 2026, register now. HMRC will write to you with the deadline for your tax return. GOV.UK says it is 3 months from the date on HMRC’s letter or email. Any tax you owe is still due by 31 January 2027. This guide sets out what changes when you register late. It comes from Wainwrights Accountants in Bromborough, Wirral. We work with clients across the UK.
Key dates if you register late
| What | Date or figure | Source |
|---|---|---|
| Deadline to tell HMRC you need to send a 2025/26 return | 5 October 2026 | GOV.UK: check how to register for Self Assessment |
| Tax return deadline if you register after 5 October 2026 | The date HMRC gives you: 3 months from the date on its letter or email | GOV.UK: Self Assessment deadlines |
| Pay the tax you owe for 2025/26 | By 11:59pm on 31 January 2027 | GOV.UK: Self Assessment deadlines |
What should you do if you missed the 5 October deadline?
Register for Self Assessment as soon as you can. GOV.UK says you must tell HMRC by 5 October if you need to complete a tax return for the previous tax year and you have either not sent a tax return before, or registered before but did not need to send one for 2024/25. For the 2025/26 tax year, which ran from 6 April 2025 to 5 April 2026, that date was 5 October 2026.
The date has passed, but the duty to register has not. GOV.UK’s wording is that if you tell HMRC after 5 October 2026, you could get a penalty.
Who needed to register by 5 October?
Anyone who has to send a 2025/26 tax return and is not already registered. GOV.UK’s list of people who must send a return includes those who, in the tax year:
- were self-employed as a sole trader and earned more than £1,000, before taking off anything you can claim tax relief on
- were a partner in a business partnership
- had to pay Capital Gains Tax when you sold or disposed of something that increased in value
- had to pay the High Income Child Benefit Charge and do not pay it through PAYE
You may also need to send one if you had untaxed income, such as money from renting out property, tips and commission, savings interest, dividends or foreign income. GOV.UK has a tool to check if you need to send a tax return.
When is your tax return due if you register late?
HMRC tells you. GOV.UK says that if you register after 5 October 2026, HMRC will send you a letter or email with a different deadline to send your tax return by, 3 months from the date on it. In law that later date applies when HMRC’s notice is dated after 31 October 2026. If it is dated on or before 31 October, an online return is still due by 31 January 2027. Go by the date HMRC gives you.
The payment date does not move. You must still pay the tax you owe by 11:59pm on 31 January 2027, or you’ll get a penalty. So if your return deadline falls after 31 January, the tax is due before the return is.
Will you get a penalty for registering late?
You may, and it depends on whether the tax is paid on time. GOV.UK says that if you register after 5 October and do not pay all of your tax bill by 31 January, you may get a “failure to notify” penalty. It is based on the amount still left to pay, and you receive it within 12 months after HMRC receives your tax return.
Separate penalties apply to a late return and to late payment. A late return gets an initial £100 penalty, with daily penalties after 3 months and further penalties after 6 and 12 months. Tax paid late gets penalties of 5% of the tax unpaid at 30 days, 6 months and 12 months, and interest is charged on the amount owed.
How do you register now?
Through GOV.UK’s check how to register for Self Assessment service. If you have registered before but did not send a tax return last year, you may need to reactivate your Self Assessment account instead. GOV.UK warns that your tax return may be delayed if you file it without reactivating an existing account.
To file online you need sign in details and your Unique Taxpayer Reference (UTR). If you are waiting for a UTR, GOV.UK has a page to check when you can expect a reply from HMRC.
Can an accountant register you and send the return?
Yes. GOV.UK has a separate route for agents to register a client, and says an agent you have authorised can deal with your tax affairs, for example submitting your Self Assessment tax return.
At Wainwrights, registering you with HMRC is included in the monthly price if you’re a new sole trader or partnership. We help other people register too, and there may be a charge. We then prepare your Self Assessment tax return from your records and file it online with HMRC. A personal tax return is from £20 a month + VAT (£24 including VAT), and the sole trader package is from £60 a month + VAT. Prices are indicative: our team confirms the scope and final price. Business prices are subject to turnover not exceeding £150,000.
No date is too late to come to us. We also take on people who are already past a deadline. To start, get a quote or book a free call.
What do people ask about registering late for Self Assessment?
Is it too late to register for Self Assessment for 2025/26?
No. You can still register after 5 October 2026. HMRC then writes to you with the deadline for your tax return, which GOV.UK says is 3 months from the date on its letter or email. The tax you owe is still due by 31 January 2027.
Do I still have to pay by 31 January 2027 if I registered late?
Yes. GOV.UK says you must still pay the tax you owe by 11:59pm on 31 January 2027 or you’ll get a penalty, even if HMRC gives you a later deadline for your tax return.
I registered years ago but stopped sending returns. Do I register again?
You may need to reactivate your Self Assessment account. GOV.UK’s registration service tells you how, and says a tax return filed without reactivating an existing account may be delayed.
Can Wainwrights register me with HMRC?
Yes. If you’re a new sole trader or partnership, registering you with HMRC is included in the monthly price. We help other people register too, and there may be a charge.
Deadlines and penalties change from one tax year to the next, and how they apply depends on your own circumstances. This guide is general information, not personal advice. To talk yours through with an accountant in Bromborough, get a quote or book a free call.