Registering Self Assessment – Who Must Register and How to Do It
Who Needs to Register for Self Assessment?
Registering for Self Assessment is the process by which you tell HMRC that you need to send a tax return, usually because some of your income is not fully taxed at source. The rules apply to a broad range of people, from sole traders and landlords to high earners and company directors.
Knowing whether you fall into one of these categories is the first step. If you are unsure, HMRC provides an online tool to check whether you need to send a return.
Who Must Register
Self-employed (turnover > £1,000), landlords (rental income > £1,000), high earners, company directors, and others with untaxed income.
How to Register
Online via GOV.UK using your National Insurance number. Takes 10-20 minutes. You’ll receive a UTR by post within 10 working days.
Key Deadlines
Register by 5 October after the tax year ends. First tax return due by 31 January following the end of the tax year (or 31 October if paper).
What You Need
NI number, personal details, income type, and business details if self-employed. Also need contact info and bank details for refunds.
Key Insights
- You must register for Self Assessment if your self-employed turnover exceeds £1,000 per tax year.
- Registration deadline is 5 October after the tax year in which you became liable.
- You’ll get a Unique Taxpayer Reference (UTR) within 10 working days of registration.
- Registration for Self Assessment and registration for self-employment happen together if you’re a sole trader.
- Missing the registration deadline may result in a penalty of £100.
- You can register online, by post (form SA1), or by phone in some cases.
- After registering, you must submit a Self Assessment tax return every year unless HMRC tells you otherwise.
| Fact | Details |
|---|---|
| Who needs to register? | Self-employed, landlords, high earners (£100k+), company directors, those with investment income > £10k, and others with untaxed income. |
| Registration method | Online via GOV.UK (recommended), form SA1 by post, or call HMRC. |
| Deadline to register | 5 October after the tax year ends (e.g., for 2024/25, register by 5 Oct 2025). |
| UTR arrival | By post within 10 working days. |
| First return deadline | 31 January (online) or 31 October (paper) after the tax year ends. |
| Penalty for late registration | £100 automatic penalty, plus potential daily penalties if further delayed. |
Self-employed individuals (sole traders)
Anyone who is self-employed, including freelancers, must register for Self Assessment if their turnover exceeds £1,000 per tax year, or they need to pay Class 2 National Insurance. Registration also triggers self-employment registration with HMRC in the same process.
Landlords with rental income
If you receive rental income above the property allowance of £1,000 per year, or you have expenses you wish to claim, you likely need to register. HMRC guidance recommends using form SA1 if you are not self-employed and your income comes from UK land and property.
Other people who may need to register
This category includes company directors, high earners with income over £100,000, those with investment income over £10,000, anyone receiving untaxed foreign income, and individuals who need to pay the High Income Child Benefit Charge. Partnership income and Capital Gains Tax liabilities are also common triggers.
How to Register for Self Assessment Online
The quickest method is to use the online registration service on GOV.UK. The process typically takes 10 to 20 minutes if you have the required details ready.
Step-by-step online registration process
Go to the GOV.UK registration page and follow the instructions. You will need your National Insurance number, personal details, and information about your income sources. The system guides you through each step.
What is the Self Assessment registration form (SA1)?
In some cases, particularly for people who are not self-employed, you may need to use form SA1. This paper form is available on GOV.UK and asks for similar information to the online process. Most registrations are now done digitally, but SA1 remains an option for those who cannot register online.
You will typically need your National Insurance number, full name, date of birth, contact details, and bank account information for any refunds. If you are self-employed, be ready with your business name, address, and the type of work you do.
Registration deadlines to keep in mind
You must notify HMRC by 5 October following the end of the tax year in which you became liable. For the 2025/26 tax year, that means registering by 5 October 2026. Missing this deadline can lead to an automatic £100 penalty.
Registering for Self Assessment as a Self-Employed Person
If you are self-employed, registering for Self Assessment and registering your self-employment with HMRC happen together. This is a single online process.
Registering your self-employment with HMRC
When you go through the online registration, you will be asked to provide details about your business. This includes the business name, address, and the nature of your trade. Once submitted, HMRC treats you as registered for both Self Assessment and self-employment.
What happens after you register?
HMRC sends you a Unique Taxpayer Reference (UTR) by post within 10 working days. You will also receive an activation code for your online account. You can then file your tax return annually. The GOV.UK guidance on registering notes that once registered, you can also estimate how much tax you might need to pay and set up monthly or weekly payments.
Differences for self-employed vs other registrants
Self-employed individuals also need to pay Class 2 and potentially Class 4 National Insurance. The registration process for landlords or company directors is similar but without the need to describe a business. For those who already have a UTR from a previous filing history, you may still need to notify HMRC again by the deadline if you need to file for the current year.
When you register for Self Assessment as a self-employed person, you are also registered for Class 2 National Insurance. If you have separate employment, check with HMRC whether you need to take any extra steps, as registration for Self Assessment does not automatically cover all NIC scenarios.
Timeline from Registration to Filing Your First Return
Understanding the sequence of events after you register helps you stay compliant. The example below uses the 2024/25 tax year.
- : Start of tax year 2024/25 – you begin earning self-employed income.
- : Deadline to register for Self Assessment (if you became liable in 2024/25).
- Within 10 working days of registration: Receive UTR number and online activation code by post.
- : Deadline to file a paper tax return for 2024/25 (if you choose paper).
- : Online tax return filing deadline and payment deadline for 2024/25.
What Is Certain and What Remains Unclear About Registration
| Established Information | Information That Remains Unclear |
|---|---|
| If you are self-employed with turnover over £1,000, you must register for Self Assessment. | The exact threshold for “trading income” may vary if you have expenses that reduce your liability – but you must still register if gross turnover exceeds £1,000. |
| Registration must be done by 5 October after the end of the relevant tax year. | Registration for Self Assessment does not automatically register you as self-employed for NIC purposes if you have separate employment – check with HMRC. |
| HMRC issues a UTR number within 10 working days of successful registration. | If you are unsure whether you need to register, HMRC provides an online tool to check. |
| Filing a tax return is mandatory after registration until you are deregistered. | — |
Why Registration Matters and the Risks of Not Registering
Self Assessment is how HMRC collects tax from people whose income is not fully taxed at source. Registering ensures you meet your legal obligations and avoid penalties. It also allows you to claim allowable expenses and pay the correct amount of tax.
Registering for Self Assessment is a broader process than registering as self-employed. When you register online as a self-employed person, you complete both registrations at once. For landlords and others, the process may differ depending on whether you already have a UTR.
Failure to register by the deadline can lead to an automatic £100 penalty. If HMRC later determines you should have registered, you may face daily penalties and interest on unpaid tax. Voluntary registration on time keeps you compliant and avoids surprises.
Sources and What Official Guidance Says
“Once you’ve registered you can: estimate how much tax you might need to pay set up monthly or weekly payments to help you budget for your bill.”
— GOV.UK
“Registering for Self Assessment refers to the process by which you tell HMRC that you need to send a Self Assessment tax return, if you do not already do so.”
— LITRG
“You must register for Self Assessment if you need to file a tax return for the more time to complete your first Self Assessment tax return.”
Summary: The Key Points About Registering for Self Assessment
Registering for Self Assessment is a straightforward process for most people, but knowing whether you need to register and meeting the deadline is essential. The threshold for self-employed individuals is £1,000 in turnover. Landlords with rental income above the property allowance must also register, typically using form SA1. After registration, you will receive a UTR and must file an annual tax return. Missing the deadline results in penalties. For further reading, you may find this guide on How to Check My Credit Score Free in Ireland Official Guide useful for related financial admin tasks. Another helpful resource is What Is a Paralegal in Ireland? Duties, Salary, and Path.
Frequently Asked Questions
Can I register for Self Assessment by phone?
Yes, you can call HMRC Self Assessment helpline to register, but the online method is quicker and more straightforward. Phone registration may take longer.
What if I miss the registration deadline?
You will likely receive a £100 penalty. You can still register late, but penalties may increase. Contact HMRC to explain your situation.
Do I need to register for Self Assessment if I’m employed but also have a side business?
Yes, if your side business turnover exceeds £1,000 (after trading allowance), you need to register for Self Assessment as a self-employed person.
How do I deregister from Self Assessment?
You can deregister when you no longer need to file returns (e.g., you stop self-employment). Use the HMRC online service or call them.
What is the Self Assessment registration form (SA1)?
SA1 is a paper form used to register for Self Assessment if you cannot register online. It is available on GOV.UK.
What happens if I already have a UTR but need to register for new income?
You may still need to notify HMRC by the deadline for the current tax year, especially if your circumstances have changed. Check with HMRC or use the ‘Check if you need to send a tax return’ tool.
Do I need to register for Class 2 National Insurance separately?
No, registering for Self Assessment as a self-employed person usually covers Class 2 NIC. If you also have employment income, confirm with HMRC that your NIC status is correct.
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