VAT UK

UK VAT number (GB): format, check digit and the post-Brexit VIES split

A UK VAT registration number (VAT Registration Number, VRN) is issued by HMRC to businesses whose taxable turnover exceeds the registration threshold (£90,000 from April 2024). The standard format is the prefix GB followed by 9 digits — usually written GB999 9999 99. Two longer variants exist: 12 digits for companies with branch traders (the last 3 are the branch identifier), and the GD/HA forms (GD + 3 digits for government departments, HA + 3 digits for health authorities).

The 9-digit core carries a check digit in the last two positions, computed with HMRC's “mod 97” algorithm: multiply the first 7 digits by weights 8,7,6,5,4,3,2, sum them, then the check is the value that makes the total a multiple of 97 (subtracting 97 repeatedly). Numbers issued after 2010 also pass a second “9755” variant where 55 is added before the mod-97 step — a valid VRN satisfies one of the two.

Brexit changed where you validate it

• GB numbers left VIES: since 1 January 2021 a GB VAT number can no longer be checked in the EU VIES system. Use HMRC's own Check a UK VAT number service instead.
• Northern Ireland keeps an EU footprint: under the Windsor Framework, NI businesses trading goods use the XI prefix, which is still validatable in VIES for intra-EU goods movements.
• This tool checks structure, not registration: a number can be syntactically valid (correct length + check digit) yet not be actively registered — only HMRC/VIES confirm live status.

Common pitfalls

• Spaces and the GB prefix: invoices show GB 999 9999 99, but APIs usually want the bare 9 digits or GB999999999. Strip spaces before validating.
• Confusing VRN with the company number: the Companies House registration number is unrelated to the VAT number.
• EORI overlap: a UK EORI often looks like GB + VAT number + 000 — they are related but not the same identifier.

FAQ

Can I still check a GB VAT number in VIES? No. Since Brexit, GB numbers are validated only via HMRC. Northern Ireland's XI numbers remain in VIES for goods.

Does a valid format mean the company is VAT-registered? Not necessarily. Format validation confirms the number is well-formed; only HMRC's live lookup confirms an active registration.

Why are some UK numbers 12 digits? The extra 3 digits identify a branch within a group registration; the 9-digit core still carries the check digit.