UTR (unique taxpayer reference)
A UTR is the ten-digit number HMRC gives you when you register for Self Assessment. It identifies you as a taxpayer, it never changes, and you cannot file a return without it.
Correct for the 2026/27 tax year. Last checked 12/09/2026.
It arrives by post, usually within a couple of weeks of registering, and it is printed on anything HMRC sends you about Self Assessment afterwards.
What it means for your money
Nothing directly, but it gates everything else. No UTR means no return, and the £100 penalty for missing 31 January applies whether or not you owed any tax. Registering in your first month of driving rather than in January is the whole of the fix.
Some platforms and agencies ask for it before they will pay you. That is a commercial requirement of theirs, not a legal one, but it means the number can hold up your first payment as well as your first return.
Where to read more
Registering as a sole trader covers the whole process, including what to do when the letter does not arrive.
Sources
Related
Registering as a sole trader: the whole process
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Self Assessment is the system HMRC uses to collect tax from people whose tax is not taken at source. You report your income and costs once a year and pay what falls out, by 31 January.
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