How to register as self-employed in the UK: a step-by-step guide

You have started invoicing clients, and someone has told you that you “need to register with HMRC.” That much is true, but it skips the part that actually matters: when the deadline falls, how the process works in practice, and what happens if you leave it too late. This guide covers all three.

When you need to register

The rule is straightforward: if your self-employment income goes over £1,000 in a tax year, you are required to register with HMRC. The UK tax year runs from 6 April to 5 April the following year, which does not line up with the calendar year, so it is worth marking the date somewhere you will actually see it.

The registration deadline is 5 October after the end of the tax year in which you started trading. If you started invoicing in November 2026, that income falls in the 2026/27 tax year, and you have until 5 October 2027 to register. That looks like a generous window, and it is, but it is also easy to let slip when there is nothing forcing you to think about it day to day.

One point that trips people up: registering is not the same as filing. Registration simply tells HMRC that you exist as a self-employed person. Your Self Assessment is the annual return where you actually report your income and expenses. You need the first before you can do the second.

If you already have a job on PAYE and start self-employed work on the side, the registration requirement still applies. Tax already being deducted from your salary does not cover your self-employed income — the two are treated as separate income streams within the same tax return.

The £1,000 figure is what HMRC calls the trading allowance, and it catches people who think of what they are doing as “a bit of freelance work on the side” rather than a business. If you sell design work on evenings and weekends, do the occasional consulting project, or run a small shop alongside a full-time job, the same threshold applies. Once you go over it, the registration obligation exists whether or not the work feels like a proper business yet.

How to register with HMRC, step by step

Registration is done online through the HMRC portal, and it costs nothing. Here is the process:

1. Set up a Government Gateway account. This is the login system for HMRC’s online services. If you already have a personal HMRC account from a previous job, you can use the same one.
2. Complete the self-employment registration form. You will be asked for your name, address, the date your business started, and a short description of what you do.
3. Confirm your National Insurance number. If you have recently moved to the UK and do not yet have one, you can still register and add it later, but apply for it as early as possible — the process can take several weeks.
4. Wait for confirmation by post. HMRC will send your Unique Taxpayer Reference, the UTR, usually within ten working days.

No supporting documents are needed at this stage — no invoices, no accounts, no business plan. HMRC only needs to know that you have started trading.

Your UTR: what it is and what to do if it does not arrive

Your UTR (Unique Taxpayer Reference) is a ten-digit number that identifies you to HMRC for the rest of your working life. You will need it every year to file your Self Assessment, so keep it somewhere you will not lose it — plenty of clients ask us for theirs months later because they cannot remember where they put it.

If more than ten working days have passed since you completed registration and the UTR still has not turned up, there are two usual causes: the letter went to an out-of-date address, or the registration did not fully go through because of a mistyped detail. Either way, the fix is the same — call HMRC’s Self Assessment helpline and ask them to check the status of your registration, rather than waiting indefinitely for post that may never come.

National Insurance for the self-employed

Alongside Income Tax, self-employed people pay National Insurance in two categories:

These are not paid separately or through a different process — they are calculated automatically as part of your Self Assessment, alongside your Income Tax. The point worth understanding is that they form part of your total tax bill, not a side cost you can leave out when working out what you owe.

What happens after you register

Once you are registered, you enter the annual Self Assessment calendar. These are the dates that matter:

• 31 January, after the end of the tax year: deadline to file your return online and pay any tax due.
• 31 July: if HMRC requires payments on account for the following year, this is the second deadline.

Payments on account deserve a mention of their own, because they catch out a lot of people the first time round. If your tax bill goes above a certain threshold, HMRC does not wait until the following year ends to collect it — it asks for two advance payments, one in January and one in July, based on what you have just declared. It is an advance, not an extra tax, but if you have not planned for it, it can double the amount you were expecting to pay in your second January as self-employed.

Your first return tends to raise the most questions, simply because it is the one time you go through the process without having done it before. After that, it becomes a matter of keeping good records through the year rather than reconstructing twelve months of invoices in January.

It also helps to know what you are actually reporting. Self Assessment covers your income and allowable expenses for the tax year, not just the profit figure you might have in your head. That means keeping a record of business mileage, equipment, software subscriptions, and anything else that is genuinely a cost of doing the work, alongside your invoices — the return only ever asks for what your records already contain.

The most common mistakes

In our years helping people set up as self-employed in the UK, the same four issues come up again and again:

Registering late. Missing the 5 October deadline can bring a penalty even if you end up owing no tax at all. HMRC penalises the late registration itself, not just late payment.

Losing track of the tax year calendar. The tax year is not the calendar year, and the January deadline arrives faster than it seems if you have not marked it from day one.

Not keeping expense records from the start. Many people only start saving receipts as the deadline approaches. By then, they have already lost months of deductible expenses they cannot reconstruct accurately.

Mixing personal and business banking. You are not required to open a separate business account as a sole trader, but running personal and business transactions through the same account means sifting through months of statements line by line come January, to work out what is deductible and what is not. A separate account, even a free one, saves that whole exercise.

None of these four mistakes is hard to avoid, but all four cost real money, or real time, when they happen.

If you have just started working for yourself in the UK, or you have been trading for a while and are not sure your registration was done correctly, book a free consultation and we will check it through with you.