What is a UTR Number?
A UTR number (Unique Taxpayer Reference) is a 10-digit number issued by HMRC to identify you as a taxpayer. Every individual and company registered for Self Assessment or Corporation Tax has one. It is unique to you and never changes.
UTR numbers look like: 1234567890
Sometimes shown with a K prefix: K1234567890
Who Has a UTR Number?
You will have a UTR number if you:
- Are registered for Self Assessment (sole traders, landlords, higher-rate taxpayers)
- Are a director of a limited company
- Have set up a limited company (the company itself has a separate UTR)
- Are registered as a CIS subcontractor
If you are employed only through PAYE and have no other income, you may not have a UTR yet. You get one when you register for Self Assessment.
Where to Find Your UTR Number
HMRC letters: Your UTR appears on almost all letters from HMRC — tax returns, tax calculations, payment reminders. Look for the reference labelled "UTR" or "Unique Taxpayer Reference."
Personal tax account: Log in at tax.service.gov.uk/personal-account. Your UTR is displayed in your account details.
Self Assessment returns: The UTR appears pre-printed on your SA100 tax return form.
If you've lost yours: Call HMRC's Self Assessment helpline on 0300 200 3310. You'll need to verify your identity. They can remind you of your UTR but will not give it to anyone else.
When Do You Need Your UTR on an Invoice?
CIS Subcontractors: Always
If you are a subcontractor under the Construction Industry Scheme, your UTR must appear on every invoice you issue to a contractor. The contractor needs your UTR to verify you with HMRC and determine the correct CIS deduction rate.
Without your UTR:
- The contractor cannot verify you as CIS registered
- They must default to the 30% deduction rate instead of 20%
- This costs you an extra 10% on every payment until the issue is resolved
Sole Traders: Sometimes
As a non-CIS sole trader, you are not generally required by law to include your UTR on invoices. However, some larger businesses and public sector bodies require it for their supplier records. Including it proactively can smooth procurement processes.
VAT-Registered Businesses
Your VAT number (separate from your UTR) is required on VAT invoices. Your UTR is not usually needed unless CIS applies.
What If You Don't Have a UTR Yet?
If you have recently started working as a sole trader or CIS subcontractor, you may not yet have a UTR. Apply immediately:
- Register for Self Assessment at gov.uk/register-for-self-assessment
- HMRC will post your UTR to your registered address within 10 working days
- Once received, add it to your FlashBill account or wherever you generate invoices
In the meantime, if a contractor asks for your UTR before it arrives, explain that you have just registered and are waiting for the number. They may agree to hold payment briefly or start at 30% with a plan to re-verify once you have your UTR.
UTR vs NI Number vs Company Registration Number
These are often confused:
| Reference | What It Is | Format |
|---|---|---|
| UTR | Tax reference for Self Assessment | 10 digits |
| NI Number | National Insurance identification | AB 12 34 56 C |
| Company Number | Companies House registration | 8 digits (e.g., 12345678) |
| VAT Number | VAT registration | GB 123456789 |
Each serves a different purpose. For CIS invoicing, your UTR is what matters.
Keeping Your UTR Secure
Your UTR is a sensitive piece of financial information. Guard it carefully:
- Never share it in unsolicited emails or phone calls
- Only provide it to genuine contractors, HMRC, or your accountant
- If you think your UTR has been misused, contact HMRC immediately
UTR in FlashBill
Add your UTR in FlashBill's account settings. It will appear automatically on all CIS invoices, ensuring contractors always have what they need to verify you at the correct deduction rate.