Short answer: You must register as self-employed with HMRC once your side hustle’s gross income tops the £1,000 trading allowance in a tax year. You register for Self Assessment online at GOV.UK, get a Unique Taxpayer Reference (UTR) by post, then file a tax return each year. The deadline to register is 5 October after the tax year you started earning, and returns are filed by the following 31 January.
Registering sounds scarier than it is. Here is the whole process, start to finish. General information for the UK, not personal tax advice.
Do you need to register as self-employed for a side hustle?
You need to register once your gross trading income passes £1,000 in a tax year. Below that, the trading allowance means you do not have to register or report. You can keep your side hustle alongside an employed job; you simply declare the extra income through Self Assessment. You do not need to form a company to do this.
How to register as self-employed (step by step)
- Go to GOV.UK. Search “register for Self Assessment” and choose the self-employed option.
- Create or sign in to a Government Gateway account. You will use this for everything HMRC.
- Enter your details. Your name, address, National Insurance number, and the date your side hustle started.
- Get your UTR. HMRC posts your 10-digit Unique Taxpayer Reference, usually within about two weeks.
- Activate your account. HMRC sends an activation code to finish setting up online Self Assessment.
- File your return each year. Report your income and expenses, and pay any tax due.
What are the key deadlines?
For income earned in the 2025/26 tax year (which ended 5 April 2026): register by 5 October 2026, then file your online return and pay by 31 January 2027. Miss the filing deadline and HMRC charges an automatic £100 penalty, so register early. See our side hustle tax guide for the full calendar.
What records will you need?
Keep a record of all income and business expenses with dates and receipts, for at least five years after the filing deadline. A simple spreadsheet is plenty when you start. Good records turn the tax return into a ten-minute job.
Frequently asked questions
Can I register as self-employed while employed?
Yes. Many people do. You keep your job and PAYE, and declare your side hustle income through Self Assessment.
How long does registration take?
Registering online takes minutes, but your UTR arrives by post in roughly two weeks, so do not leave it to the last minute.
Do I need to register if I earn under £1,000?
No. The £1,000 trading allowance means you do not need to register or report below that.
General information, not tax advice. Register and confirm details at GOV.UK. The Finances Toolkit includes a tax reserve calculator to set money aside as you earn.