Going self-employed? You must tell HMRC by 5 October

If you started working for yourself in the last tax year, you must register with HMRC by 5 October. Miss it and you can be fined before you owe any tax.

Most people know about the 31 January tax return. Far fewer know about 5 October. If you started a side hustle or went self-employed at any point in the last tax year, this is the date you tell HMRC you exist. Miss it and you can be penalised for the registration alone, before a penny of tax is even due.

The short version

• If you became self-employed in the 2025 to 2026 tax year, you must tell HMRC by 5 October 2026.
• This is about registering, not paying. The tax itself is not due until 31 January 2027.
• You need to register if your gross self-employed income was over £1,000 in the year.
• Registering late can trigger a penalty even if you end up owing little or no tax, because the fine is for not telling HMRC in time.
• Register early: your Unique Taxpayer Reference arrives by post, and you cannot file your return without it.

Why 5 October exists, and who it applies to

The 5 October deadline is the date you have to notify HMRC that you have income to declare. It applies if you became self-employed, started a side business, or began earning untaxed income in the last tax year and have not registered before.

The tax year runs to 5 April. So if you started working for yourself at any point between 6 April 2025 and 5 April 2026, your deadline to register is 5 October 2026.

Registering is not the same as paying. It just puts you in the system so you can file a Self Assessment return. The return, and the tax, come later.

Do you actually need to register?

You need to register if your gross self-employed income was more than £1,000 in the tax year. That is income before expenses, not profit.

If you earned £1,000 or less from self-employment, the trading allowance usually means you do not have to tell HMRC at all. It is worth understanding how that works if you are running a side hustle alongside a job.

There are exceptions. You still need to register even under £1,000 if you want to claim a loss, pay voluntary National Insurance, or use your self-employment income to claim Tax-Free Childcare or Maternity Allowance.

The penalty people do not see coming

Here is the part that catches people out: HMRC can charge a penalty for registering late even if your tax bill is small.

The fine is for the failure to notify, not for the tax. It is based on the tax you owe and how late you are, so the longer you leave it, the worse it gets. Someone who registers a year late on a modest side income can still face a charge out of all proportion to the tax itself. Leaving it is one of the most common tax mistakes the newly self-employed make.

Telling HMRC on time is free. Telling them late is not.

Register early, not on 4 October

Leaving it to the deadline is a mistake, because registering is not instant.

When you register, HMRC sends you a Unique Taxpayer Reference, or UTR, by post. You cannot file your Self Assessment return without it, and it does not arrive the same day. Register on 4 October and find the UTR slow, and you can end up unable to file when January comes.

Register as soon as you know you need to. Our guide on whether you need to register for Self Assessment as a sole trader covers exactly who has to and how, and your first 90 days self-employed walks through the wider setup.

What happens after you register

Once you are registered you are in the Self Assessment system, and the rest of the year has its own dates.

• You file a return for the 2025 to 2026 tax year by 31 January 2027.
• You pay any tax owed by the same date.
• If your bill is over £1,000, you may also start making payments on account.

None of that is due in October. October is just the door you have to knock on first. The self-employed tax calendar lays out everything that follows.

Common questions

What is the 5 October deadline for?

It is the date you must tell HMRC you became self-employed or started earning untaxed income, so you can be set up for Self Assessment. For income earned in the 2025 to 2026 tax year, the deadline is 5 October 2026.

Do I need to register if I only made a few hundred pounds?

Usually not. If your gross self-employed income was £1,000 or less, the trading allowance generally means you do not have to register. You might still choose to, for example to pay voluntary National Insurance or claim a loss.

Is registering the same as paying my tax?

No. Registering just puts you in the system. Your return and any tax for 2025 to 2026 are not due until 31 January 2027.

What happens if I register late?

HMRC can charge a failure-to-notify penalty. It is based on the tax you owe and how late you are, so it grows the longer you wait, and it can apply even when the tax itself is small.

How long does it take to get set up?

Not instant. HMRC posts you a Unique Taxpayer Reference after you register, and you cannot file without it, so leave time rather than registering right on the deadline.

The bottom line

The 5 October deadline is easy to miss because nobody sends you a reminder. If you started working for yourself in the last tax year and earned more than £1,000, register now. It is free, it is quick, and doing it late can cost you a penalty before you owe any tax at all.

Once you are in the system, every other date matters too. Our guide to your first 90 days self-employed covers registering and what comes next, and the self-employed tax calendar keeps the rest of the year in view.

This is general guidance, not tax advice. Your own circumstances decide what you need to do, so check your position on gov.uk or with an accountant before you act.