When to Register for Self Assessment
You must register for Self Assessment by 5 October after the end of the tax year in which you first need to file. For example, if you started a business in June 2026, you must register by 5 October 2026.[1]
Don’t leave it until the deadline — registration can take several weeks because HMRC sends your UTR and activation code by post.
If You’re Self-Employed
This is the most common registration route. You can do it entirely online:[2]
- Go to gov.uk/register-for-self-assessment
- Sign in with your Government Gateway account (or create one)
- Select “self-employed” as the reason for registering
- Enter your personal details, National Insurance number, and business details
- Submit your registration
If You’re Not Self-Employed
If you need to file for other reasons (rental income, capital gains, High Income Child Benefit Charge, etc.), the process is slightly different:[3]
- Online — register through your Government Gateway account
- By post — complete form SA1 and send it to HMRC
What You’ll Need
Have these ready before you start:[1]
- Your National Insurance number
- Your full name, date of birth, and address
- Your email address and phone number
- If self-employed: the date you started trading and the nature of your business
After Registering
Once HMRC processes your registration, you’ll receive:[4]
- Your UTR (Unique Taxpayer Reference) — a 10-digit number sent by post, usually within 10 working days (21 days if you’re abroad)
- An activation code — sent separately, usually within 7 working days, which you use to activate your HMRC online account
Keep your UTR safe. You’ll need it every time you file a return, make a payment, or contact HMRC about your Self Assessment. Treat it like a bank account number.
Registration Deadlines and Penalties
If you register late, you won’t automatically be penalised for the late registration itself. However, late registration often leads to late filing — and late filing penalties start at £100 on 1 February (the day after the 31 January deadline).[4]
The sooner you register, the more time you have to set up your online account, gather your records, and file comfortably before the deadline.
Tip: If you’re newly self-employed, register straight away rather than waiting until October. It costs nothing and gives you plenty of time.
Frequently Asked Questions
When is the deadline to register for Self Assessment?
You must register by 5 October after the end of the tax year in which you first need to file. For example, if you started a business in June 2026, register by 5 October 2026.
How do I register for Self Assessment if I am not self-employed?
If you need to file for rental income, capital gains, or the High Income Child Benefit Charge, register online through your Government Gateway account or by posting form SA1 to HMRC.
How long does it take to get my UTR number after registering?
HMRC usually sends your UTR (Unique Taxpayer Reference) by post within 10 working days, or 21 days if you are abroad. An activation code for your online account arrives separately within about 7 working days.
Is there a penalty for registering late for Self Assessment?
Late registration itself does not carry an automatic penalty, but it often leads to late filing, and late filing penalties start at £100 on 1 February if you miss the 31 January deadline.
Further Reading
- Your UTR Number: What It Is and How to Find It
- Setting Up Your Government Gateway Account
- How to File Your Self Assessment Tax Return
- What is Self Assessment?
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