Working for yourself and not sure whether HMRC needs to know? The test is simple. Add up everything you were paid for self-employed work in the tax year, before you take any costs off. If that figure is over £1,000, you have to register for Self Assessment. If it is £1,000 or less, you almost certainly do not.

The £1,000 test, in detail

A tax year runs from 6 April to 5 April. HMRC looks at your gross self-employed income across that period, meaning the total that came in before expenses.

This catches people out. Say you made £1,600 selling handmade cards and spent £900 on materials and stall fees. Your profit was only £700, but your gross income was £1,600, so you are over the line and have to register. The £1,000 figure is about turnover, not what you kept.

The allowance that creates this threshold is called the trading allowance. If your gross self-employed income is £1,000 or less, the allowance covers it in full. You do not have to tell HMRC, you do not pay tax on it, and you do not file a return for it. Keep a basic record of what you earned in case that ever changes, and that is all.

Other situations where you have to register

The £1,000 rule is the common one, but you also need to register for Self Assessment if any of these apply:

If you are only employed and pay tax through PAYE, none of this applies and you have nothing to do.

Having a job as well does not change the answer

A lot of people assume a side income is fine because their main job already deducts tax. It is not. If your self-employed income clears £1,000, you register, regardless of what you earn from an employer. Both sets of income go on the same return, and the tax you already paid through your payslip is credited against the final bill. There is more detail in registering when you already have a job.

The deadline

You must register by 5 October following the end of the tax year you started trading.

So if you took your first self-employed payment at any point between 6 April 2025 and 5 April 2026, your deadline to register is 5 October 2026. Started in the current tax year instead? You have until 5 October 2027.

Do not confuse this with the 31 January filing date. Registering by 5 October is about telling HMRC you exist as a taxpayer so they can set you up. Filing the return and paying the tax come later, by the following 31 January.

How registering works

You register online through the "Register for Self Assessment" service on GOV.UK. It takes about ten minutes and you need your National Insurance number, your address, the date you started, and a short description of the work. The step-by-step version is here.

HMRC then posts you a Unique Taxpayer Reference, a ten-digit number you use every time you file or pay. It usually arrives within about ten working days. You cannot file a return without it, which is the main reason not to leave registration until January.

What you are signed up for once you register

From that point HMRC expects a Self Assessment return from you every year until you tell them you have stopped. You file even in quiet years where you earned very little.

Registering also switches on your National Insurance as a self-employed person. Class 2 is £3.65 a week for 2026 to 2027, but if your profit is £7,105 or more it is treated as paid without you handing anything over, so your state pension record still builds. Class 4 is 6% on profit between £12,570 and £50,270, then 2% above that. Both are worked out on your return and collected with your tax, not billed separately during the year.

If you are already past 5 October

Register now anyway. HMRC can charge a late notification penalty, but it is based on the tax you owed and on you coming forward before they contact you. For an honest, unprompted disclosure the penalty is often reduced to nothing. Waiting makes it worse, not better. See registering late for what to expect.