Last updated: 14 October 2026
When do you need to register for Self Assessment?
If you need to file a tax return for the first time, you must register with HMRC by 5 October after the end of the tax year. For income in 2026/27, which ends on 5 April 2027, the deadline is 5 October 2027. You need to register if, for example, you started self-employment with income over £1,000, received untaxed income such as rent, or had income over £100,000 not taxed through PAYE. Registering late can lead to a penalty if tax is unpaid.
Who needs to register
| Situation | Register? |
| Self-employed with gross income over £1,000 | Yes |
| Partner in a business partnership | Yes |
| Rental income over £1,000 | Yes |
| Untaxed savings or investment income over £10,000 | Yes |
| Dividends over £10,000 | Yes |
| Capital gains you need to report | Yes, or use the real-time CGT service |
| High Income Child Benefit Charge not paid through PAYE | Yes |
| Employee with all income taxed through PAYE | Usually no |
How to register
- Self-employed: register online as self-employed, which sets you up for Self Assessment and Class 4 NIC. You’ll get a Unique Taxpayer Reference (UTR) by post.
- Not self-employed: register online with form SA1, for example for rental income.
- Partners: register the partnership and each partner.
Allow time: UTRs can take up to 15 working days in the UK, or longer if you’re abroad.
Penalties for registering late
If you register late but file and pay by 31 January, there’s usually no penalty. If tax is unpaid because you didn’t notify HMRC, a failure to notify penalty can apply, based on the unpaid tax and whether the failure was deliberate. It can be reduced to nothing if you tell HMRC within 12 months and the failure wasn’t deliberate.
Example
Liam started a window cleaning business in June 2026 and earned £14,000 by April 2027. He must register by 5 October 2027, file his 2026/27 return by 31 January 2028 and pay any tax by then. If he waits until December 2027 to register, files on time and pays in full, he’s unlikely to be penalised.
Making Tax Digital
From 6 April 2026, sole traders and landlords with qualifying income over £50,000 must use MTD-compatible software and send quarterly updates. The threshold falls to £30,000 from April 2027 and £20,000 from April 2028. New businesses should check whether they’ll be in scope.
Key dates for 2026/27 income
| Date | Deadline |
| 5 October 2027 | Register for Self Assessment |
| 31 October 2027 | Paper return |
| 31 January 2028 | Online return, balancing payment and first payment on account for 2027/28, if due |
Keep records from the start
Once you start trading or letting, keep sales invoices, receipts and bank statements in one place. Opening a separate bank account for the business makes your first return much easier.
Frequently asked questions
Do I need to register if I made a loss?
Yes, if you’re self-employed, to record the loss.
What if I’ve registered before?
Reactivate using your existing UTR.
Can my accountant register for me?
Yes, once authorised.
Can I register before the year ends?
Yes, as soon as you start.
Related: whether a director with no income needs a return, registering for National Insurance and landlord tax returns.
Talk to Accotax
Want this handled for you? Our team at Accotax can help with Self Assessment registration. See our small business accountants service, or contact us for a free, no-obligation quote.
This page is general guidance based on HMRC rules for the 2026/27 tax year, checked against gov.uk on 14 October 2026. It is not personal advice, so speak to an accountant about your own situation.
