Common structure

Prefix: two letters, the code of the issuing country.
Number: an identifier that is unique in that country, up to 15 alphanumeric characters (European Commission).

United Kingdom (GB) and Northern Ireland (XI)

Numbers starting with GB or XI are the prefix followed by 12 or 15 digits, according to HMRC's input pattern. The same page also says 14 characters, which fits only the 12-digit case; we accept both lengths. HMRC's service accepts them with or without spaces and in uppercase or lowercase (HMRC pattern). Example shape (illustrative): GB123456123456. For where each prefix applies, see GB, XI and EU numbers.

EU countries: what the Commission document says

The table shows what the Commission's national implementation document of 28 June 2022 states. It does not cover every country, and national rules may have changed since: confirm with the national customs authority (source).

Country	Format as stated
Belgium (BE)	BE + 10-digit Crossroads Bank for Enterprises number for Belgian operators; other categories have other lengths
Denmark (DK)	DK + CVR number
France (FR)	FR + SIRET for French operators; other formats for non-EU operators
Netherlands (NL)	NL + 9 digits, based on the fiscal number and padded with leading zeros if shorter
Portugal (PT)	PT + NIF (tax identification number) for domestic operators; other formats for non-EU operators
Romania (RO)	RO + up to 15 alphanumeric characters; other formats for non-EU operators and TIR carnet holders

For the other EU countries the document does not state a structure. In that case rely on the general rule above (two-letter code plus up to 15 alphanumeric characters) and confirm in the official service.

Check a number

Use the format checker on the home page, then confirm registration with the official service.