If you started earning money outside your normal payslip at any point between 6 April 2025 and 5 April 2026, you might need to tell HMRC by 5 October 2026. Miss it, and a penalty can follow even before you've filed a single return.
Most people who miss this deadline aren't trying to dodge anything. They just didn't know it existed. The January filing deadline gets all the attention, but registration is a separate, earlier step, and it catches out first-time sole traders and landlords every single year.
Who actually needs to register
You need to register for Self Assessment if, during the 2025/26 tax year, any of the following applied to you and you haven't filed a return before:
- You earned more than £1,000 from self-employment or freelancing, including side hustles
- You earned rental income above the £1,000 property allowance
- You made capital gains above £3,000, for example from selling shares or a second property
- You received other untaxed income, such as certain foreign income or commission
If none of that applies, you're probably fine. If any of it does, and this is your first time, the clock is already running.
What happens if you miss it
Registering late doesn't automatically mean a fine. But if HMRC decides you should have told them and didn't, a "failure to notify" penalty can apply, calculated as a percentage of any tax you owe. Even if the eventual bill is small, it's an unnecessary risk for something that takes a few minutes to fix.
There's also a knock-on problem: once you register, HMRC needs to issue your Unique Taxpayer Reference (UTR) before you can file anything, and that can take 10 working days or longer. Registering close to the January filing deadline instead of now just adds pressure you don't need.
What to do now
- Check the list above honestly against your last 12 months
- If you're unsure whether your side income counts, register anyway. There's no downside to registering and later confirming you didn't owe anything
- Register through HMRC's online service, you'll need your National Insurance number and some basic details about your income
- Once registered, keep a note of your UTR somewhere safe. You'll need it every year from here on
None of this needs to be complicated. It's one form, a bit of information about what you've earned, and then it's done until January.
If working out whether you need to register (or what to do once you have) feels like more admin than you want to take on, that's exactly what we're here for.