How to Register for Self Assessment: The Step-by-Step UK Guide

Before You Start

If you've started a side hustle, freelance business, or began earning untaxed income over £1,000, you must tell HMRC. Before you open the official website, make sure you have these details ready.

The 'What You Need' List:

Your National Insurance (NI) Number: (Found on payslips or the HMRC app)
Business Start Date: When did you first earn money?
Personal Details: Full name, address, and date of birth.
Business Contact Info: Telephone number and email address.

The Registration Steps

The process is entirely online and takes about 15 minutes to complete. Follow these steps carefully:

Action Plan: Get Registered

Set up a 'Government Gateway' account: This is your secure digital ID for all UK government services.
Log in to the HMRC portal: Once logged in, choose the option to "Register for a tax."
Select 'Self Employment': (Even if it's just a small side hustle like Vinted or Etsy).
Fill out the form (SA1 or CWF1): Provide your business name (can just be your own name) and your start date.
Review and Submit: Double-check your address, as your UTR will be sent there in the post.

Go to GOV.UK Registration

What Happens After?

Once you hit "Submit," your work is done for about two weeks. Here is what you should expect to see in your letterbox.

The Short Answer

You will receive your UTR number in the post.

HMRC will send you a 10-digit code called a 'Unique Taxpayer Reference' (UTR). You can't even start a tax return without it. It usually arrives within 10-14 working days.

In Plain English

What is "UTR (Unique Taxpayer Reference)"?

This is your 10-digit 'Tax DNA'. It identifies you to HMRC for life. Once you have it, you'll use it every single year when you file your return.

The Registration Timeline

Timing is everything in tax. If you miss these windows, the computer automatically issues fines.

Important Deadlines:

5 October: The absolute latest you should notify HMRC you've started trading.
31 January: The final deadline to file your online return and pay your bill.
Trading Allowance: If you earned under £1,000 total, you don't even need to do any of this.

Common Registration Errors

The 'Wait Until January' Trap: Trying to register in late January. You won't get your UTR in time to file, resulting in an automatic £100 fine.
Double Registration: Registering again because you didn't receive your letter yet (this creates a mess in the HMRC system).
Incorrect Address: Forgetting to update your address with HMRC before registering.

Your Next Step

While you wait for your UTR to arrive, start preparing your records so the actual filing is easy.

While You Wait...

Check out our Allowable Expenses guide to see what you can deduct.
Read about the £1,000 Trading Allowance for small side hustles.
If you sell on platforms, see our Vinted & Etsy Tax rules.

Return to Hub

Frequently Asked Questions

It typically takes 10 working days for your UTR to arrive in the post. HMRC will send it to the address they have on file for you.

Yes, registering for Self Assessment is completely free. Be careful of 'copycat' websites that try to charge you a fee for this service.

If you miss the Oct 5th deadline, register as soon as possible. HMRC rarely issues penalties for late registration if you still file and pay on time (by Jan 31st).

If you register but your income stays under £1,000, you can usually tell HMRC and they will 'close' the request for a return. However, if they still send you a notice to file, you MUST file it (even with zeroes) to avoid a late penalty.

Tax Disclaimer: TaxWiz provides general educational information and guides for UK residents. While we strive to maintain accuracy for the 2026/27 tax year, tax rules are subject to change. This content does not constitute regulated financial, legal, or tax advice. For complex situations, we strongly recommend consulting a qualified UK accountant. View our full Disclaimer.