PayToolkit › When Do I Need to Register for Self Assessment?

When Do I Need to Register for Self Assessment?

The 5 October registration deadline explained, who actually needs to file, and what happens if you miss it.

Short answer: you must register for Self Assessment by 5 October following the end of the tax year in which you first had income that needs declaring — for example, by 5 October 2027 for income earned in the 2026/27 tax year (6 April 2026 to 5 April 2027).

Who actually needs to register

You need to register if any of the following applied to you in the tax year:

You earned more than £1,000 from self-employment or freelance/side-hustle work (before expenses)
You earned income from renting out property
You received dividend income above your dividend allowance
You had untaxed savings or investment income
You need to pay the High Income Child Benefit Charge (household income over £60,000 and someone claims Child Benefit)
You had Capital Gains Tax to pay on the sale of property, shares or other assets
You're a company director without all your income taxed through PAYE
HMRC has sent you a notice to file, for any reason

If none of these apply — for example you're only employed under PAYE with no other income — you generally don't need to register.

Worked example

Sarah started dog-walking on the side in June 2026, alongside her full-time employed job. By April 2027 she'd earned £3,400 from it. Because that's over the £1,000 trading allowance, she must register for Self Assessment by 5 October 2027 and file her return online by 31 January 2028, paying any tax owed by the same date. Use the Sole Trader Tax Calculator to see roughly what she'll owe, and the Tax Set-Aside Calculator to work out how much to put by from each job.

Common mistakes

Waiting until January to register. Registering late doesn't remove your obligation to file and pay on time — it just leaves you scrambling for your Unique Taxpayer Reference (UTR), which can take up to 10 working days to arrive by post.
Thinking the £1,000 trading allowance means no registration needed. The allowance can reduce your taxable profit to zero, but if HMRC has asked you to file, or other criteria apply, you may still need to register and file a return.
Forgetting rental income counts too, even if it's a spare room or a single buy-to-let running at a small profit.

What happens after you register

HMRC sends you a UTR and sets up your Self Assessment account. You'll then file a return each year by 31 January (online) covering the previous tax year, and pay any tax owed by the same date. If your bill is over £1,000, you may also need to make Payments on Account towards the following year.

Sole Trader Tax CalculatorEstimate your Income Tax and NICs Tax Set-Aside CalculatorKnow how much to save from each payment PAYE + Side Hustle CalculatorCombine employed and self-employed income Expense TrackerLog income and expenses year-round, free

Sources: GOV.UK — Register for Self Assessment. This page is general guidance, not personalised tax advice.

Frequently asked questions

Do I need to register if I only earned £500 from a side hustle?▾

Not necessarily — the trading allowance covers up to £1,000 of gross income from self-employment before you need to register or declare it, unless HMRC has separately asked you to file.

What's the deadline to register for Self Assessment?▾

5 October following the end of the tax year in which you first became liable — for the 2026/27 tax year (6 April 2026–5 April 2027), that's 5 October 2027.

What happens if I register late?▾

You can still register after 5 October, but you risk a ‘failure to notify’ penalty if tax is owed and you file or pay late as a result. Registering as soon as you know you need to avoids this.

Do I need to register every year?▾

No — once registered, you keep the same UTR and file annually until you tell HMRC you no longer need to (for example, if you stop self-employment).