If you’re self-employed, work under the CIS scheme, or earn extra income outside of PAYE — you need to register for Self Assessment with HMRC. But registering isn’t always straightforward. Whether you’re just getting started or missed the deadline last year, this guide will walk you through how to register for Self Assessment in 2025, what documents you need, and how to avoid delays with your Unique Taxpayer Reference (UTR) number.
What Is Self Assessment?
Self Assessment is how HMRC collects Income Tax from people who don’t have it automatically deducted from their wages (like employees do through PAYE).
You’ll need to register if you:
- Are self-employed or a sole trader
- Work under the Construction Industry Scheme (CIS)
- Earn money from property, crypto, dividends, or side gigs
- Receive over £1,000 in untaxed income during the tax year
Once registered, you’ll file a Self Assessment tax return every year.
When to register for Self Assessment (Key Deadlines)
If you started working for yourself in the 2024/25 tax year (6 April 2024 to 5 April 2025), you must register with HMRC by 5 October 2025.
Deadline to register: 5 October
Deadline to file your return: 31 January 2026
Deadline to pay your tax: 31 January 2026
Late registration can result in penalties, delays in getting your UTR, and missing out on refunds.
Step-by-Step: How to Register for Self Assessment
Step 1: Gather Your Details
Before registering, make sure you have:
- Full name and date of birth
- National Insurance (NI) number
- Address and contact info
- The date you started self-employment
- Your business type (sole trader, CIS worker, etc.)
Step 2: Choose Your Registration Method
There are three main ways to register, depending on your situation:
| Your Status | Registration Route |
|---|---|
| New sole trader | Register for Self Assessment online via HMRC |
| CIS subcontractor | Register as self-employed and for CIS at the same time |
| Previously registered but stopped | Re-register using form CWF1 or online login |
Step 3: Register Online via HMRC
Visit: https://www.gov.uk/register-for-self-assessment
You’ll need to:
- Set up a Government Gateway account
- Complete the online form (CWF1 for self-employment)
- Submit your application
After registering, HMRC will send your Unique Taxpayer Reference (UTR) by post within 10 working days (or 21 days if you’re abroad).
What is a UTR number and why you need it?
Your UTR is a 10-digit number used by HMRC to identify you for Self Assessment. You’ll need it to:
- Submit your tax return
- Join the Construction Industry Scheme (CIS)
- Get paid by contractors
- Claim tax refunds
If you’re registering late, apply now — UTR delays can prevent you from filing and claiming refunds.
Registering for Self Assessment as a CIS subcontractor
If you work in construction under the CIS scheme, you should:
- Register as self-employed AND for CIS at the same time
- Provide contractor details if possible
- Expect a 20% tax deduction on your income (until you file)
After filing your return, you may be owed a CIS tax refund — especially if you earned below the personal allowance threshold.
Can I register for Self Assessment through Tax2u?
Yes, Tax2u makes registration quick, simple, and stress-free. We’ve helped thousands of construction workers, sole traders, and side hustlers register with HMRC and claim their UTR.
With Tax2u, you get:
- Online UTR application in 3 simple steps
- Free guidance from our UK-based tax team
- Automatic reminders and updates
- Full setup for Self Assessment and CIS if needed
Start your Self Assessment registration
Don’t risk missing the deadline or delaying your refund. Registering for Self Assessment only takes a few minutes and the earlier you do it, the smoother your tax year will be.
Apply for your UTR and register now with Tax2U