HMRC Self Assessment Number (UTR): What It Is and How to Find It
Your HMRC self assessment number is your Unique Taxpayer Reference (UTR). Here's what it is, where to find it, how to get one, and why you need it for Making Tax Digital and CIS.
The short answer
Your 'HMRC self assessment number' is your Unique Taxpayer Reference (UTR) — a 10-digit number HMRC gives every self assessment taxpayer. Find it on any HMRC letter (SA250 'Welcome to Self Assessment', tax return, or statement), in your HMRC online account, or on the HMRC app. If you've never registered, you get a UTR by registering for self assessment at gov.uk, which usually takes about 10 working days for the number to arrive by post.
If you've been asked for your "HMRC self assessment number", that's your Unique Taxpayer Reference (UTR) — and it's one of the most important numbers in your tax life. Here's what it is, where to find it, and why it matters for Making Tax Digital and CIS.
What is a UTR?
A UTR is a 10-digit number HMRC issues to every person or business registered for self assessment. It uniquely identifies you to HMRC. You'll see it referred to as your:
- "self assessment number",
- "tax reference",
- "unique taxpayer reference", or simply
- "UTR".
On some payslips and payment references it appears with a "K" on the end
(e.g. 1234567890K) — that's the payment version, but the number itself is the
10 digits.
Where to find your UTR
You already have a UTR if you've ever registered for self assessment. Look on:
- HMRC letters — the SA250 "Welcome to Self Assessment", your notice to file a return, statements of account, or payment reminders.
- Your previous tax return or its calculation.
- Your HMRC online account — sign in with your Government Gateway ID and go to the Self Assessment section.
- The HMRC app — your UTR is shown in your account details.
Tip: your UTR never changes. Once you've got it, store it somewhere safe — you'll use it for every tax return, every MTD quarterly update, and for CIS.
How to get a UTR if you don't have one
If you've never been in self assessment:
- Register for self assessment at gov.uk (as self-employed, a landlord, or another reason to file).
- HMRC sets up your record and posts your UTR, usually within about 10 working days (allow longer if you're overseas).
- You'll also be enrolled to file online.
You cannot use MTD for Income Tax, and a contractor can't properly verify you for CIS, until you have a UTR — so register early.
UTR vs National Insurance number
These get confused constantly, so to be clear:
| UTR | National Insurance number | |
|---|---|---|
| Format | 10 digits (e.g. 1234567890) | 2 letters, 6 digits, 1 letter (e.g. QQ123456C) |
| Purpose | Self assessment & tax | Your NI contributions record |
| Issued by | HMRC when you register for SA | HMRC/DWP, usually before age 16 |
For MTD and CIS you'll typically need both.
Why your UTR matters for MTD and CIS
- MTD for Income Tax: your UTR (with your National Insurance number) identifies you on your digital records, quarterly updates and final declaration.
- CIS: contractors verify subcontractors with HMRC using the UTR. A verified, registered UTR means you're deducted at 20%; without one you're deducted at 30%. Gross payment status (0%) is also tied to your UTR and compliance record.
Getting set up in ThisQuarter
When you add yourself or a client in ThisQuarter, you enter the UTR and National Insurance number once. From there the app uses them to retrieve business details, obligations and CIS deductions from HMRC and to submit your quarterly updates and final declaration — all from a secure, encrypted desktop app.
This article is general information, not tax advice. You can register for self assessment and check your details at gov.uk.
Frequently asked questions
What is my HMRC self assessment number?
It's your Unique Taxpayer Reference (UTR): a 10-digit number HMRC issues to everyone registered for self assessment. It identifies you (or your business) on your tax return, quarterly MTD updates, and CIS records. It sometimes appears with a 'K' on the end on payment references.
Where do I find my UTR number?
On HMRC letters such as the SA250 'Welcome to Self Assessment', your tax return or notice to file, statements of account, and payment reminders. It's also in your HMRC online (Government Gateway) account under Self Assessment, and on the HMRC app.
How do I get a UTR number?
Register for self assessment at gov.uk. Once registered, HMRC posts your UTR, usually within about 10 working days (longer if you're abroad). You can't use MTD for Income Tax or register for CIS without one.
Is a UTR the same as a National Insurance number?
No. Your National Insurance number (e.g. QQ123456C) is for your NI record. Your UTR is a separate 10-digit number just for self assessment and tax. You'll often need both for MTD and CIS.
Do I need my UTR for CIS?
Yes. Contractors verify subcontractors with HMRC using their UTR, and it determines your deduction rate. Without a verified UTR you're deducted at the higher 30% rate instead of 20%.
Related reading
How to Check Your CIS Deductions Under MTD for Income Tax
A step-by-step guide to checking the CIS deductions HMRC holds against you as a subcontractor, reconciling them with your contractor statements, and getting them right before your final declaration.
MTD for CIS Subcontractors: What Subbies Need to Know for 2026
How Making Tax Digital for Income Tax affects CIS subcontractors (subbies). When you're in scope, what quarterly updates involve, and how your CIS deductions fit into your tax bill.