Registering as self-employed: the deadline, the UTR and what happens next

Start trading now, register once you pass £1,000

Nothing stops you quoting, invoicing and getting paid before you have registered. The requirement begins once your gross income for a tax year is more than £1,000, and registering as a sole trader means registering for Self Assessment.

You need a National Insurance number before you start. If you are already registered for Self Assessment for another reason, you still register again as a sole trader, so that you are registered for Class 2 National Insurance.

Once registered you are in the system, so a later year at £1,000 or less does not automatically take you out of it: you can tell HMRC you have stopped being self-employed, and some sole traders choose to stay registered to keep their National Insurance record intact.

The notification deadline: 5 October

You must tell HMRC by 5 October after the end of the tax year. This is a legal deadline rather than an HMRC convention: the rule is that you tell HMRC within six months of the end of the tax year in which your self-employment profits first became chargeable to tax.

For the 2025-26 return, that date is 5 October 2026. It applies if you have never sent a tax return before, or if you registered previously but did not need to send a return for 2024-25.

Filing for that year comes later than the notification date: paper returns for 2025-26 are due by 11:59pm on 31 October 2026, and online returns by 11:59pm on 31 January 2027. If you want the bill collected through your tax code instead of paid directly, the return has to be in by 11:59pm on 30 December 2026.

If you register late

Registering after 5 October does not stop you filing. HMRC sends a letter or email giving you a new filing deadline of three months from the date on it.

The bill keeps its own date. Your tax for the year is still due by 11:59pm on 31 January 2027 even though the filing deadline moved, so a late registration can leave you a short window between filing and paying.

You could also get a penalty. The failure-to-notify penalty can be charged if you register after 5 October and do not pay all of your tax by 31 January. It is based on the amount still left to pay and is issued within 12 months after HMRC receives your return, and the percentage depends on your behaviour and whether you told HMRC unprompted. A non-deliberate failure reported unprompted within 12 months falls in the 0% to 30% range.

There is no penalty where you have a reasonable excuse, the failure was not deliberate, and you told HMRC without unreasonable delay once the excuse ended.

The UTR, and what you do with it

Registering produces a Unique Taxpayer Reference, a 10-digit number that HMRC may simply call your tax reference. You will usually get it by post around 15 days after you register, and it takes longer if you live overseas.

You need the UTR to sign in and file your return online, and to quote when you deal with HMRC about your tax. If it has not turned up, it is in your Personal Tax Account and the HMRC app, and on previous tax returns and other HMRC documents such as notices to file and payment reminders.

When you pay, your payment reference is the 10-digit UTR followed by the letter K, 11 characters in total. The wrong reference delays the payment or sends it against another tax bill, which is the sort of problem that only shows up when a reminder arrives.