If you are self-employed, earn income outside of PAYE, or run your own business in the UK, you need to register for Self Assessment with HMRC so you can file a tax return each year. The process is straightforward: you sign up online through the Government Gateway, receive a Unique Taxpayer Reference (UTR) number, and then file your return by the deadline. This guide walks you through every step in plain English, so you know exactly what to do, what to expect, and when to do it.
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What is Self Assessment and Who Needs to Do It?
Self Assessment is the system HMRC uses to collect Income Tax from people whose tax is not automatically deducted through PAYE (Pay As You Earn). Instead of your employer handling it, you are responsible for working out how much tax you owe and paying it yourself.
You will need to register for Self Assessment if, in the last tax year, any of the following applied to you:
- You were self-employed as a sole trader and earned more than £1,000 (before expenses)
- You were a partner in a business partnership
- You earned more than £100,000 in total income
- You received untaxed income, such as rental income, tips, or commission
- You earned income from abroad
- You received Child Benefit while you or your partner earned more than £50,000 (the High Income Child Benefit Charge threshold)
- You were a company director
- You had Capital Gains to report
If you are unsure whether this applies to you, HMRC has a simple tool on GOV.UK, where you can check your situation.
How Do I Register with HMRC for Self Assessment?
The most common way to register is online through the HMRC website. The steps differ slightly depending on whether you are self-employed or registering for another reason.
Step 1 – Create a Government Gateway Account
Before you can register, you need a Government Gateway account. This is the online portal HMRC uses for all its digital services.
Go to the GOV.UK Self Assessment registration page and click “Sign in” or “Create sign-in details.” You will be asked to provide your email address and create a password. HMRC will send you a Government Gateway User ID — keep this safe, as you will need it every time you log in.
If you already have a Government Gateway account from a previous interaction with HMRC (for example, for VAT or PAYE), you can use that same account.
Step 2 – Register as Self-Employed or for Self Assessment
Once you have your Government Gateway account, you need to complete the relevant registration form.
If you are self-employed (sole trader): Use the form SA1 or register through the “Register for Self Assessment” section in your HMRC online account. You will need to confirm the date you started self-employment, your business activity, and some personal details.
If you are not self-employed but have untaxed income: Use form SA1, which you can complete and submit online through your HMRC account.
If you are a new partner in a partnership, the nominated partner must register the partnership using form SA400, and each partner registers using form SA401.
Step 3 – Wait for Your UTR Number
After you register, HMRC will send a letter to your registered address containing your Unique Taxpayer Reference (UTR) number. This is a 10-digit number that identifies you in the tax system. You will use it every time you submit a return or contact HMRC about your tax affairs.
How Do I Register as Self-Employed for the First Time?
If this is your first time working for yourself, registering as self-employed is the place to start. You do not need an accountant or any specialist knowledge to do this — you just need to do it promptly.
When Should You Register?
You must register by 5 October following the end of the tax year in which you became self-employed. For example, if you started self-employment on 1 June 2024, you must register by 5 October 2024.
Registering late can result in a penalty, so it is always better to do it as soon as you start earning self-employed income — even if you are unsure whether you will earn more than the £1,000 trading allowance.
What Information Do You Need to Register?
Before you start, have the following to hand:
- Your full legal name and date of birth
- Your National Insurance (NI) number
- Your home address and contact details
- The name of your business (if different from your own name)
- The nature of your business (a brief description of what you do)
- The date you started self-employment
What Happens After You Register as Self-Employed?
Once HMRC has processed your registration, you will receive:
- Your UTR number by post (within 10 working days for UK addresses)
- An Activation Code for your HMRC online account (if this is your first time using it)
- An online account where you can file returns, check your tax position, and communicate with HMRC
You will also need to register for Class 2 and Class 4 National Insurance contributions, which are handled as part of the Self Assessment process — so you do not need to do this separately.
If your self-employed turnover exceeds £90,000 (as of the 2024/25 tax year), you will also need to register for VAT. This is a separate registration from Self Assessment.
How Long Does It Take to Register with HMRC for Self Assessment?
One of the most common questions people ask is how quickly the process is completed. The honest answer is that it depends on how you register and when.
Online Registration
If you register online, HMRC will typically process your application and send your UTR number within 10 working days if you have a UK address. If you are registering from abroad, allow up to 21 days.
The online process itself only takes around 10 to 20 minutes to complete, as long as you have all your details ready.
Postal Registration
If you choose to register by post (using paper forms), the process takes longer. You should allow at least 3 to 4 weeks for HMRC to receive, process, and respond to a postal registration.
What If You Are Registering Close to the Deadline?
If the 31 January Self Assessment filing deadline is approaching and you have not yet received your UTR number, do not panic. HMRC will take into account the registration date, and there is a process for requesting your UTR if it has not arrived. In some cases, HMRC can issue UTR numbers by phone for people who are urgently trying to file.
To avoid this situation, always register as soon as you know you need to file a return, ideally, well before October of the relevant tax year.
How Do I Get My UTR Number for the First Time?
Your UTR (Unique Taxpayer Reference) is issued automatically once you register for Self Assessment. You do not need to apply for it separately — it is part of the registration process.
Where Will You Find Your UTR?
Your UTR will arrive in a letter from HMRC, posted to the home address you used when registering. The letter is usually titled “Your Unique Taxpayer Reference” or it may appear on a letter about your tax return.
Your UTR can also be found in the following places:
- In your HMRC online account under “Self Assessment” — once your account is activated
- On any previous Self Assessment tax return you have filed
- On letters or notices sent by HMRC about your tax affairs
- On payslips from HMRC if you have made previous payments
What If You Have Lost Your UTR Number?
If your letter has gone missing or you cannot find your UTR, you can retrieve it by:
- Logging in to your HMRC online account at GOV.UK — your UTR will be shown in your Self Assessment section
- Calling HMRC on 0300 200 3310 — have your NI number and personal details ready for identity verification
- Using the HMRC app — your UTR is displayed within the app once you are logged in
HMRC will not email your UTR for security reasons, so if you need a written copy, you will need to request a letter or access it through your online account.
What Are the Self-Assessment Tax Deadlines You Need to Know?
Once you are registered, these are the key dates to keep in mind every tax year:
| Deadline | What It Covers |
|---|---|
| 5 April | End of the tax year |
| 5 October | Register for Self Assessment (if new) |
| 31 October | Deadline for paper tax returns |
| 31 January | Deadline for online tax returns AND payment of tax owed |
| 31 July | Second payment on account (if applicable) |
Missing these deadlines, particularly 31 January, will result in an automatic £100 penalty, even if you have no tax to pay. Further penalties and interest apply the longer a return remains unfiled.
What Do You Need to File a Self Assessment Tax Return?
Registering is only the first step. When it comes to actually filing your return, you will need records of:
- All income you received in the tax year (self-employment, employment, rental, dividends, etc.)
- Business expenses you want to claim against your self-employed income
- Bank interest and any savings income
- Pension contributions made during the year
- Gift Aid donations, which can increase your tax refund
- P60 or P45 if you were also employed during the year
Keeping clear, organised records throughout the year makes filing much easier and helps ensure you do not pay more tax than you owe.
Can an Accountant Register for Self Assessment on Your Behalf?
Yes. If you find the process confusing or simply do not have the time, a registered accountant or tax adviser can handle your Self Assessment registration and filing on your behalf. They will act as your “agent” with HMRC, which means they can communicate directly with HMRC, submit returns, and deal with any queries.
To authorise an agent, you need to sign a 64-8 form (which can now be done digitally through HMRC’s online services). Your accountant will then be able to manage your Self Assessment account on your behalf.
Using a professional is particularly worthwhile if your tax affairs are complex — for example, if you have multiple income sources, rental properties, overseas income, or you are claiming significant business expenses.
What Happens If You Miss the Registration Deadline?
If you miss the 5 October registration deadline, you should still register as soon as possible. HMRC will not usually impose a penalty for a late registration if you file and pay your tax on time by 31 January, but it is important to act quickly.
If you have been self-employed for more than one year without registering, you may have tax and National Insurance that has built up. HMRC can charge interest and penalties on unpaid tax, so the sooner you sort this out, the better. In many cases, HMRC is reasonable about unprompted disclosures — coming forward voluntarily almost always results in a better outcome than being contacted by them first.
Our experts handle your tax return properly the first time, making sure everything is filed correctly and on time so you never worry about HMRC again.
The Bottom Line
Registering for Self Assessment does not have to be stressful. Here is a quick recap of what you need to do:
- Check whether you actually need to register (most self-employed people do)
- Create a Government Gateway account at GOV.UK
- Register using the appropriate form for your situation
- Wait for your UTR number to arrive by post (up to 10 working days)
- Activate your HMRC online account using the code sent to you
- File your tax return and pay any tax owed by 31 January
If you are new to Self Assessment and are not sure where to start, speaking to an accountant can save you time, stress, and potentially money. At Cheap Tax Returns, we help sole traders, freelancers, and small business owners across the UK handle their Self Assessment registration and tax returns quickly and affordably — so you can get on with running your business.
Disclaimer: The information provided on Cheap-TaxReturns.co.uk is for informational purposes only and should not be considered as financial advice. Always consult with a professional accountant to ensure compliance with UK laws and regulations.
