Quick answer
A Unique Taxpayer Reference (UTR) is a 10-digit number HMRC gives you when you register for Self Assessment. You get it by registering online, and it arrives by post, usually within 10 working days (21 if you live abroad).
Updated October 2026 · Figures based on 2026/27 rates
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How to apply
Register for Self Assessment on GOV.UK using a Government Gateway account. Choose the option that matches your situation, such as self-employed or a new source of income, and HMRC will set up your record.
What happens next
HMRC posts your UTR and an activation code to the address they hold. You use the code to activate your online Self Assessment account, and the code expires after 28 days, so act quickly.
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If you have lost your UTR
Look on previous returns, HMRC letters or your online tax account. You can also ask HMRC for it online or by phone. Never share it publicly, since it identifies your tax record.
When to register
You must register by 5 October after the end of the tax year in which you first needed to file, for example by 5 October 2026 for the 2025/26 tax year.
What a UTR is used for
Your UTR identifies your Self Assessment record. HMRC uses it to match your return, payments and correspondence to you rather than to someone with a similar name. You will need it when you file, when you pay a Self Assessment bill, when you contact HMRC about your return and, for some people, when you give your details to a contractor or a letting agent.
The number is different from your National Insurance number. Your National Insurance number follows you through your working life, while a UTR is issued only when you register for Self Assessment. Not everyone has one. Employees whose tax is fully handled through PAYE usually do not.
A worked example: a side business that creates a filing duty
This is an illustrative example, not a real client. Ben is employed and earns a salary taxed through PAYE. In the 2025/26 tax year he also starts selling restored furniture and makes a profit of £14,000 after costs. His turnover is above the £1,000 trading allowance, and he has not already registered, so he has to register for Self Assessment and file a return.
| Item | Working | Amount |
|---|---|---|
| Profit from the side business | Sales less costs | £14,000 |
| Personal Allowance | Already used by salary | nil left |
| Income Tax on the profit | £14,000 x 20% (basic rate, if his total income is below £50,270) | £2,800 |
| Class 4 NI | (£14,000 – £12,570) x 6% | £85.80 |
Because his salary already uses his Personal Allowance, the whole £14,000 profit falls into the basic-rate band for Income Tax, while Class 4 only applies to profits above £12,570. Ben’s total bill on the side business is therefore £2,800 + £85.80 = £2,885.80, before any other adjustments. He has until 5 October 2026 to register, and until 31 January 2027 to file online and pay. Because he is registering for the 2025/26 tax year, he should allow time for the UTR to arrive by post.
Common mistakes
- Leaving registration until the last week before 5 October, then missing the 31 January filing deadline because the activation code has not arrived.
- Registering twice and ending up with two records. Check your HMRC online account first.
- Throwing away the letter. Keep the UTR and activation code safe, and note that the code expires after 28 days.
- Sharing the UTR in public places such as social media or unsecured emails.
- Assuming you do not need to register because the business is small. The trading allowance of £1,000 can help, but income above it normally needs to be reported.
A short checklist
- Check whether you already have a UTR on old returns, letters or your online tax account.
- If not, register on GOV.UK using a Government Gateway account.
- Wait for the UTR and activation code, usually up to 10 working days, or 21 if you live abroad.
- Activate your online Self Assessment account within 28 days of receiving the code.
- Diarise 31 January for filing and payment.
Related guides
Our guide on how to register for Self Assessment walks through the steps, while who needs to register helps you decide whether you must. Read how to set up a Government Gateway account if you do not yet have one, and what happens if you miss the deadline if you are running late. Sole traders can also see our service page for sole traders.
SATR can help you register and then prepare the return for a fixed fee from £199 + VAT. Our qualified UK accountants file everything online.
This is general information, not personal tax advice.
Keeping your UTR and records safe
Treat your UTR like any other piece of financial identity. It is not a password, but together with other personal details it can be used by fraudsters to pose as you. Store the original HMRC letter somewhere secure, and keep a note of the number in a password manager or similar secure place rather than in an open email thread.
Be cautious about unexpected texts, emails or calls that ask for your UTR, a refund claim or a payment. HMRC does not ask you to share personal information through unsolicited links. If you are unsure, go directly to the official GOV.UK page or your online tax account and contact HMRC using the details there.
Once you hold a UTR, make a habit of keeping the related records together: your Government Gateway user ID, the year you first registered, your filing confirmations and your payment receipts. Self Assessment records should be kept for five years after the 31 January filing deadline for the relevant tax year, so a tidy folder pays off if HMRC ever asks a question or you need to prove your income for a mortgage or loan.
If you stop trading or no longer need to file, you should tell HMRC rather than simply ignoring the return notices that may continue to arrive. Our guide on how to deregister from Self Assessment explains the process.
Frequently asked questions
Do I need a UTR if I am an employee?
Not usually. You need one only if you have to file a Self Assessment return, such as for untaxed income or rental profits.
Can an accountant register for me?
Yes. We can handle registration and get you set up for filing once you receive your UTR.
What if my UTR has not arrived after 10 working days?
Check that you used the correct address, then contact HMRC. If you live abroad, allow up to 21 working days. You can usually find the number in your online tax account once you have activated it.
Is a UTR the same as a company number?
No. A UTR is a 10-digit tax reference. Limited companies have their own Companies House number and also a separate company UTR for Corporation Tax.
Do I get a new UTR every year?
No. Your UTR stays the same, so keep a note of it. You use it each year when you file.
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The Bottom Line
Your UTR is the 10-digit key to your Self Assessment account: register on GOV.UK, wait for the letter (usually within 10 working days), and activate your account within 28 days. Leave it too late and you will miss the 31 January filing and payment deadline — so register as soon as you know you need to file.
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