Starting a side hustle raises a question that trips a lot of people up: at what point do you officially become self-employed?
It doesn’t happen automatically. And whether you need to register depends on a few key factors.
The trigger point
If your trading income — that’s income from selling goods or services — exceeds £1,000 in a tax year, you are required to tell HMRC. The way you do that is by registering for Self Assessment as a sole trader. (HMRC — Check if you need to tell HMRC about your income from online platforms)
A tax year runs from 6 April to 5 April the following year.
What is Self Assessment?
Self Assessment is HMRC’s system for collecting income tax on earnings that haven’t been taxed at source — like the income from a side hustle. Each year, you complete a tax return declaring your income and allowable expenses. HMRC uses this to calculate what you owe. (HMRC — Self Assessment tax returns)
The registration deadline
If you need to register for Self Assessment for the first time, the deadline is 5 October following the end of the tax year in which you had untaxed income. So if you earned more than £1,000 from a side hustle in the 2024/25 tax year (which ran to 5 April 2025), you should have registered by 5 October 2025. (HMRC — Check how to register for Self Assessment)
Miss that deadline and you risk a penalty.
What if I have a regular job?
Having a PAYE job — one where your employer deducts tax from your wages — does not automatically cover your side hustle income. Your employer handles tax on your employment income only. Income from self-employment is entirely separate and is your responsibility to declare. (HMRC — Tax Help for Hustles)
How to register
You can register for Self Assessment online through GOV.UK. Once you’ve registered, HMRC will send you a UTR — a Unique Taxpayer Reference. This is the number you’ll use on your tax return. The process can take up to 10 working days to receive your activation code, so it’s worth doing well ahead of any deadline. (HMRC — Check how to register for Self Assessment)
Not sure if you need to register?
Use HMRC’s free online tool to check. It takes just a few minutes and uses your specific circumstances to give you a clear answer. If the answer is yes, the sooner you register the better.
Use our free UK side hustle tax calculator to find out whether your income triggers a Self Assessment requirement — and how much tax you’d owe.