How is a UTR check digit calculated?

Take the nine body digits, multiply them by the weights 6,7,8,9,10,5,4,3,2, sum the products and take the total modulo 11. Subtract that remainder from 11; a result of 11 maps to check digit 2 and 10 maps to 1. The answer must equal the printed first digit.

How many digits is a UTR?

A UTR is exactly 10 digits. It is sometimes printed with a trailing 'K' on correspondence, but the number itself is the 10 digits, with the first digit acting as a check digit.

Does a valid check digit mean the UTR is active?

No. A valid check digit confirms the number is internally consistent under HMRC's algorithm, not that it is registered or active. Only HMRC can confirm a UTR is live for a given taxpayer.

Where do I find my UTR?

Your UTR appears on the 'Welcome to Self Assessment' letter, on previous tax returns, on statements of account and in your HMRC online account under Self Assessment details.

Is my UTR sent anywhere?

No. The check digit is computed entirely in your browser using JavaScript. The UTR you enter is never uploaded or stored.

UK UTR (Tax Reference) Validator

A Unique Taxpayer Reference (UTR) is the 10-digit number HMRC issues to identify a taxpayer for Self Assessment and Corporation Tax. Accountants and freelancers need to confirm a UTR is well-formed before filing returns or quoting it on forms. This free validator runs HMRC’s check-digit algorithm in your browser so a transposed digit is caught instantly.

How it works

The first digit of a UTR is a check digit derived from the other nine using a weighted modulus-11 scheme:

Strip non-digits so you have 10 digits.
Take the nine “body” digits (positions 2–10 of the printed UTR).
Multiply each by its weight: 6, 7, 8, 9, 10, 5, 4, 3, 2.
Sum the products and compute the total mod 11.
Subtract the remainder from 11. If the result is 11 the check digit is 2; if it is 10 the check digit is 1; otherwise it is the result itself.
The UTR is valid if this computed check digit equals the printed first digit.

The tool displays the weighted sum, the mod 11 remainder and both the expected and printed check digits so you can see exactly why a number passed or failed.

Notes

A valid check digit confirms the UTR is internally consistent, not that it is registered or active — only HMRC can confirm that. A failed check almost always means a single digit was mistyped or transposed. Everything runs locally; your UTR never leaves your device.