A Unique Taxpayer Reference number, usually called a UTR, is a ten-digit code HMRC assigns to identify you or your company for tax purposes. You get one when you register for Self Assessment or set up a limited company, and it stays with you for life. Once issued, the same number follows you through every return, payment, and letter, even if you stop trading for years and later come back into the system.
What a UTR Looks Like
A UTR is typically ten digits, though HMRC systems also accept a 13-digit version that includes legacy formatting characters.1GOV.UK. Unique Taxpayer Reference – HMRC Patterns for Services On HMRC letters it may appear simply as “tax reference” rather than the full name.2GOV.UK. Find Your UTR Number
Unlike a Company Registration Number, which is public and appears on invoices and filings, a UTR is confidential. Don’t share it on social media, invoices, or anywhere publicly visible. HMRC will never ask for it by email or text, so any unsolicited request for your UTR is likely a scam.
Personal UTR vs Company UTR
Individuals and limited companies each get their own separate UTR, and the two are not interchangeable. A sole trader or someone with rental income gets a personal UTR tied to their Self Assessment record. A limited company gets a company UTR tied to its Corporation Tax record. A company director who also files a personal Self Assessment return will hold both. Filing a Corporation Tax return with a personal UTR, or the other way round, will cause HMRC to reject the submission.
Who Needs a UTR
You need to register for Self Assessment, and therefore get a UTR, if any of the following applied in the previous tax year:
- You were self-employed and earned more than £1,000 before tax relief.
- You were a partner in a business partnership, regardless of income.
- You owed Capital Gains Tax on the sale or disposal of an asset.
- You or your partner had individual income over £60,000, received Child Benefit, and have not chosen to pay the High Income Child Benefit Charge through PAYE.
- You are repaying a student or postgraduate loan through Self Assessment.
You may also need to register if you received £2,500 or more of untaxed income from sources like rental properties, savings and investment interest, dividends, tips, commissions, or foreign income.3GOV.UK. Self Assessment Tax Returns – Who Must Send a Tax Return The £60,000 threshold for the High Income Child Benefit Charge applies from the 2024/25 tax year onward.4GOV.UK. High Income Child Benefit Charge
Trusts also need a UTR once they become liable for Income Tax, Capital Gains Tax, Inheritance Tax, or Stamp Duty Land Tax, and trustees must register the trust before filing a return for it.5GOV.UK. Register a Trust as a Trustee
How to Register and Get Your UTR
Which form you use depends on why you need a UTR. If you are registering as self-employed, use form CWF1 through the GOV.UK online service. For any other reason (rental income, foreign income, capital gains, the High Income Child Benefit Charge), use form SA1 instead. You can submit SA1 online or print it and post it to HMRC.6GOV.UK. Register for Self Assessment if You Are Not Self-Employed
Before you start, gather your National Insurance number, full legal name, date of birth, and current address. If you are registering as self-employed, you’ll also need the date your business activities began. HMRC checks these details against existing government records, so any mismatch can hold things up.
After you submit, HMRC posts a letter to your registered address with your new UTR. It normally arrives within about 15 days.2GOV.UK. Find Your UTR Number Postal applications take longer. A separate activation code for the Government Gateway online filing service usually follows shortly after.
The 5 October Registration Deadline
If you need to file a Self Assessment return for the previous tax year and you have either never filed before or did not file last year, you must tell HMRC by 5 October. To file a return covering the 2024/25 tax year (6 April 2024 to 5 April 2025), for example, the registration deadline is 5 October 2025.7GOV.UK. Check How to Register for Self Assessment
Registering after 5 October does not push back the 31 January payment date. You still owe any tax due by 31 January, and if you register late HMRC gives you a filing deadline of three months from the date of their letter or email rather than the standard 31 January.8GOV.UK. Self Assessment Tax Returns – Deadlines Missing the payment date means interest accrues at 7.75% as of January 2026.9GOV.UK. HMRC Interest Rates for Late and Early Payments Late filing carries its own penalty ladder starting at an automatic £100, rising quickly the longer the return is outstanding.10GOV.UK. Self Assessment Tax Returns – Penalties
How to Find a UTR You’ve Lost
If you registered before but can’t remember your UTR, check any previous correspondence from HMRC. The Notice to File a Tax Return (form SA316), prior Self Assessment returns, and statements of account all show the number. You can also find it by signing into your personal tax account on GOV.UK, or through the HMRC app using your Government Gateway credentials or biometric login.2GOV.UK. Find Your UTR Number
If none of that works, call the Self Assessment helpline. Have your National Insurance number ready, because HMRC will use it to verify your identity before disclosing any account details.11GOV.UK. Self Assessment – General Enquiries