Unique Taxpayer Reference
United Kingdom · Individuals and companies
Paste or type the number — punctuation is optional.
Other identifiers
Europe
Asia and the Middle East
Oceania
What this check does — and what it cannot do
This tool checks the number's structure and its check digit, using the published algorithm for that document. A number that passes is well formed: it is arithmetically consistent and could have been issued.
It cannot tell you whether the number was actually issued, whether it is active, or who it belongs to. Only the issuing tax authority can confirm that, through its own lookup service. Treat a passing result as "worth submitting", never as proof of identity.
The generator produces numbers that satisfy the same checksum, for filling forms while developing and testing software. They are arithmetic, not records: they are not drawn from any register and do not correspond to a real holder. No generator is offered for the US Social Security Number.
How the UTR check works, and what the number tells you
A UTR is an identifier for people and businesses issued in United Kingdom. This page checks one against the published rule, shows which specific test it fails when it fails, and decodes the facts the digits carry. Everything runs in your browser — the number you type is never sent anywhere.
How it works
- Applies the published checksum rather than only checking the length and shape.
- Names the exact rule that failed, so a typo is distinguishable from a number that was never valid.
- Decodes what the number encodes: check digit.
- Generates valid test numbers, for fixtures and for exercising your own validation code.
10 digits: the check digit comes first weights 6 7 8 9 10 5 4 3 2 over the last nine digits check = (11 - (sum mod 11)) mod 11 A remainder of 1 would need a check digit of 10, which does not fit in one character, so those bodies are simply never issued.
Worked example
Checking 4886161233, a valid UTR, digit by digit.
- input 4886161233
- normalised 48861 61233
- Check digit 4
- Checksum Weighted mod 11 — the de facto algorithm, not officially published
- result passes every published check
The checksum passes, so the number is internally consistent, and the tool reads off check digit. Internal consistency is not the same as the number being issued to somebody — see the note below.
Reading the result
- HMRC has not published this algorithm. The weights above are the de facto version implemented in Xero, FreeAgent, Sage and most open-source tax libraries, and the tool labels the result accordingly rather than presenting it as official.
- A passing checksum means the digits are consistent with each other, not that the number exists. Only United Kingdom's own registry can tell you whether a number was actually issued and is still valid, and no offline tool can substitute for that.
- The check happens entirely in your browser. Nothing is uploaded, logged, or stored, which matters more here than on most tools because these numbers are personal data in every jurisdiction that issues them.
- Punctuation is ignored. Spaces, dots, dashes and slashes are stripped before the check, so a number pasted in any common local format is read the same way.
Common questions
- My number is real but this says it is not valid. Why?
- Check for a transposed pair of digits first — that is the single most common cause, and every checksum here is designed to catch it. Failing that, the number may predate the current rule: several countries changed or introduced their checksum at a known date, and older numbers were not reissued. If the tool names a specific rule that failed, that is the one to look at.
- Does a valid result mean the number is registered?
- No, and this is the limit worth understanding. A checksum proves the digits are mutually consistent, which catches typos and made-up numbers. It cannot prove the number was issued, is still active, or belongs to the person quoting it. Only the issuing authority's own lookup can do that.