If you’ve started self-employment, begun renting out a property, or received untaxed income during the 2025/26 tax year, you must register for Self Assessment with HMRC by 5 October 2026. Registration tells HMRC you need to file a return and triggers your Unique Taxpayer Reference (UTR) — without it, you can’t submit your return or pay tax owed for the year.
In this comprehensive guide, we will break down the 2026 registration process, explain the new digital requirements, and ensure you have all the tools necessary to meet the mandatory deadlines.
Do You Need to Register for Self Assessment?
Only some people in the UK have to complete a tax return, but if they do, they have to register for it. In general, there are several different categories in which you will have to register for Self Assessment:
- Self-Employed/Sole Traders: If you have made over £1,000 profit from self-employment in the tax year.
- Renters: If you earn income from the rental of land.
- High Earners: If you’re taxed entirely through PAYE with no other income, income level alone no longer triggers Self Assessment. HMRC removed the previous £150,000 threshold from the 2024/25 tax year onward. You’ll still need to register if you have untaxed income on top of PAYE, such as dividends, savings interest, or rental income.
- Untaxed income: Income that has not been taxed on a taxable basis, such as a saving, an investment or a dividend.
- Capital Gains: If you have sold assets that you own (such as a second home, shares, or other chargeable assets) and your total gains exceed the £3,000 annual exempt amount for 2025/26.
- Child Benefit: If you or your partner have income above a threshold (usually £60,000 – £80,000 depending on the current Child Benefit tapering rates) and you receive payments of Child Benefit.
If in any doubt, it’s better to check early. Penalties can be severe if you are required to be registered but do not register, even if you do not end up owing tax.
Already Registered Before? What to Do Instead
If you have previously submitted a Self Assessment tax return but stopped (for instance you returned to PAYE for a few years) you do not have to “register” as you would if you were a brand new taxpayer.
Instead, you should:
- Find your old UTR: Your 10-digit Unique Taxpayer Reference (UTR) is the same for life.
- Re-activate your account: Sign in to your online HMRC services. If your account has been inactive, you might need to contact HMRC to let them know that you are self-employed once again so that they can reopen your account.
- Sign-in method: If you already have a Government Gateway account, keep using it. HMRC has confirmed existing account holders won’t be affected until HMRC contacts them directly, which isn’t expected before late 2027. GOV.UK One Login currently only applies to brand-new individual customers signing up from scratch.
The Registration Deadline: 5 October
Timing is everything. The deadline for registering for Self Assessment for 2025/26 is 5 October 2026.
This deadline can be mistaken for the filing deadline (31 January). The October deadline, however, is a particular deadline to advise HMRC that you need to file. If you miss this, HMRC will have less time to provide you with your UTR and activation codes, meaning that you may experience a frantic rush in January. You should not leave it until the last minute, so note 5th October in your diary as the latest date to send your registration form in.
Two other dates worth noting alongside registration: paper tax returns for 2025/26 must reach HMRC by 31 October 2026, while online returns and any tax owed are due by 31 January 2027.
What You’ll Need Before You Start
Before you sit down to complete the online form, gather the following documentation to ensure the process is smooth and uninterrupted:
- National Insurance Number: This is found on your payslip, P60 or on the NI app.
- Full Personal Details: Your current address, date of birth, and contact information.
- Business Details: If you are a sole trader, you’ll need your business name, start date, and business address.
- Identity Documents: If you’re a new individual customer signing up via GOV.UK One Login (this doesn’t apply to most self-employed sole traders, see below), have your UK passport, photocard driving licence, or biometric residence permit ready.
- Records of Income: Rough estimates of what you expect to earn can help HMRC categorise your account correctly.
Government Gateway and GOV.UK One Login
In 2026, the way we access government services is gradually changing. From 9 February 2026, HMRC began directing brand-new individual customers (people with no existing Government Gateway account) to sign up via GOV.UK One Login instead.
Important for self-employed readers: sole traders aren’t classed as “individuals” for this purpose. If you’re registering as self-employed, you’ll continue to use Government Gateway to register and file, not GOV.UK One Login. If you already have a Government Gateway account from previous tax years, keep using it. HMRC will contact you directly if and when you need to move across.
Step-by-Step: How to Register for Self Assessment
Follow these steps to register for Self Assessment via the official HMRC portal:
- Visit GOV.UK: Navigate to the “Register for Self Assessment” page.
- Sign in or create an account: Self-employed sole traders use Government Gateway; brand-new individual customers registering for another reason (e.g. property income) may be directed to create a GOV.UK One Login.
- Choose your category: Specify whether you are registering as a sole trader, a partner in a business, or for another reason (e.g., high income or property).
- Complete the correct HMRC form for your situation:
• CWF1 if you’re a self-employed sole trader (this also registers you for Class 2 National Insurance)
• SA1 if you’re not self-employed but need to register for another reason, such as being a company director or having untaxed income
• SA400 (to register the partnership) and SA401 (for each individual partner) if you’re in a business partnership
Each form asks for your NI number, relevant start date, and nature of income. - Review and Submit: Double-check all entries. An error in your NI number or address can delay your UTR by weeks.
- Verify via Email: You will receive a confirmation email that your application has been received.
What Happens After You Register
After submitting your application, HMRC will act on the information. A letter will be sent to you in the mail within 10-15 working days, with the possibility of a longer delay during peak times (September and October).
The Unique Taxpayer Reference (UTR) is included in this letter. This 10-digit number is essential as you will have to use it for filing your tax return and paying your tax. After obtaining a UTR, you will be able to log in to your GOV.UK account and view your Self Assessment dashboard which includes payments deadlines, payments, and eventually, filing your return.
How to Deregister from Self Assessment If Your Circumstances Change?
If you stop being self-employed, close your business, or your income drops below the mandatory thresholds, you must inform HMRC to “deregister”. If you simply stop filing without telling them, HMRC will assume you are late and start issuing automatic £100 penalties.
To deregister:
- Log into your HMRC online account.
- Navigate to “Stop Self Assessment”.
- Provide the date your self-employment ended or the reason you no longer need to file.
- Ensure you still file a “final” return for the year you were active to settle any remaining tax.
How MyIVA Can Help
Navigating tax registration can feel like a lot to manage on top of running your business or juggling multiple income sources. At MyIVA, our accountants can register you for Self Assessment, take care of the ongoing filing, and make sure you never miss a deadline. If you’re newly self-employed, we can also help you get set up for Making Tax Digital ahead of the relevant threshold, and if a tax bill catches you off guard, we can talk you through your payment options with HMRC. Whether it’s a one-off Self Assessment return or ongoing support throughout the year, we’re here to take the admin off your plate so you can focus on your work.
FAQs: Frequently Asked Questions
Can someone register for Self Assessment on my behalf?
Yes, an authorised tax agent or accountant can register you, but you remain legally responsible for the accuracy of the information provided.
How does registering for Self Assessment work with Making Tax Digital (MTD ITSA)?
Making Tax Digital for Income Tax (MTD ITSA) became mandatory from 6 April 2026 for self-employed people and landlords with qualifying income over £50,000. The threshold drops to £30,000 from April 2027. If you’re above the relevant threshold, HMRC will require you to keep digital records and submit quarterly updates through compatible software instead of a single annual return. Registering for Self Assessment is still the first step either way.
What’s the most common mistake people make when registering?
The most common mistake is waiting until the last minute. If you try to register for Self Assessment on 4 October and encounter a technical issue with your sign-in or identity verification, you may miss the deadline.
How long does registration take?
The online form takes about 15–20 minutes, but receiving your UTR by post usually takes 2 weeks.
What if I miss the 5 October deadline?
You should still register as soon as possible. While there is a potential penalty for late notification, HMRC is often lenient if you register quickly and file/pay your tax on time by January.
Do I need a National Insurance number to register?
Yes, it is a primary requirement for the registration form. If you don’t have one, you must apply for an NI number first.
Can I register if I live outside the UK?
Yes. If you have UK-based income (like rental income from a UK property) while living abroad, you must still register and file a return.
Conclusion
Registering for Self Assessment is a fundamental part of running a business or managing significant wealth in the UK. By following this 2026 guide, you can ensure that you meet the 5 October deadline, navigate HMRC’s sign-in requirements correctly, and secure your UTR well in advance of the January filing rush.
Don’t let the paperwork deter you from your professional goals. With the right preparation and the support of services like MyIVA when things get tough, you can manage your tax obligations with confidence. For more information on navigating the complexities of UK tax and debt, stay tuned to the MyIVA blog.
