Registering as a sole trader means telling HMRC you're self-employed so you can be sent a Self Assessment tax return each year. You don't register a 'business' — there's nothing to file with Companies House. The whole process is one form, but HMRC sends paper letters with your UTR, so plan for a 10-working-day wait before you can fully use the system.
Direct answer
It's free, takes about 15 minutes online, and you only need a Government Gateway account and your National Insurance number. Here's exactly what to do — and the mistakes that delay people by weeks. Use the key facts, step list and official source links on this page to confirm the decision before you spend money or register anything.
- Cost
- £0
- Time online
- ~15 min
- UTR arrival
- 10 working days
- Deadline
- 5 Oct after tax year
Checklist
Quick checklist
- Find your National Insurance number
- Recover or create a Government Gateway login
- Pick a start date for self-employment
- Register at gov.uk/register-for-self-assessment
- Wait for UTR letter (up to 10 working days)
- Activate online account with the second letter
- Open a dedicated business bank account
- Set up a simple spreadsheet or use FreeAgent / QuickBooks
Section 01
When you must register
Legally, you must register for Self Assessment by 5 October following the tax year in which you started trading. The UK tax year runs 6 April to 5 April. So if you started self-employed work in June 2025, the deadline to register is 5 October 2026.
- Trading income over £1,000 in a tax year — register.
- Trading income under £1,000 — covered by the trading allowance, no need to register.
- You can register earlier if you want a UTR for invoices, bank accounts or grant applications.
- Missing the 5 October deadline doesn't fine you automatically, but missing the 31 January filing deadline does (£100 + daily charges).
Section 02
What you need before you start
- National Insurance number — on your payslip, P60, or in the HMRC app.
- A Government Gateway user ID and password (you can create one during sign-up).
- Personal details — full name, address, date of birth.
- The date you started self-employment.
- A description of your work (just a sentence — 'freelance graphic designer', 'plumber').
- An email address you check often (HMRC sends some confirmations digitally).
Section 03
The actual registration — step by step
- 01
Go to gov.uk/register-for-self-assessment
Choose 'Sole trader' (not 'Partner' or 'Not self-employed'). The page is gov.uk/register-for-self-assessment/sole-trader.
- 02
Sign in or create a Government Gateway account
If you've ever done a Self Assessment, used the HMRC app, or claimed tax-free childcare, you already have one — recover the credentials rather than creating a duplicate.
- 03
Confirm your identity
HMRC will ask for two pieces of evidence — usually NI number plus a passport, P60 or recent payslip. If you have no UK credit history this is the bit that most often fails; have a passport ready.
- 04
Fill in the SA1/CWF1 form
If you're newly self-employed it's the CWF1 (Class 2 NI included). If you only need Self Assessment for other reasons it's the SA1. The online flow picks the right one automatically.
- 05
Submit and wait for your UTR
Your Unique Taxpayer Reference (UTR) is a 10-digit number that arrives by post within 10 working days. You cannot file a return without it. A second letter follows with your Self Assessment activation code.
- 06
Activate your online account
Use the activation code within 28 days. After that you can log in at gov.uk/log-in-file-self-assessment-tax-return and you're set.
Section 04
Common reasons registration fails or stalls
- Address mismatch — your address on the form must match HMRC's records (often your last P60 address).
- No UK passport — identity verification often loops; you may have to call 0300 200 3310.
- Already registered — many people register, forget, then re-register; check the HMRC app first.
- Letters going to a parents' address — change your address with HMRC before registering, not after.
Section 05
What changes the day you're registered
Practically, very little. You can keep working, invoicing and being paid the same way. The differences are: you'll get a Self Assessment return each April; you'll owe income tax and Class 2/4 National Insurance on profit; and HMRC may ask for payments on account (advance instalments) once your bill exceeds £1,000.
- Keep every invoice, receipt and bank statement for 5 years after the 31 January submission deadline.
- Open a separate bank account — not legally required, but it saves hours at year-end.
- Set aside roughly 25–30% of profit for tax and NI as you go.
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Common questions