A SIRET is the 14-digit identifier France assigns to every business establishment. It combines the company-level SIREN (first 9 digits) with a 5-digit NIC (Numéro Interne de Classement) that pins down the specific site. Procurement teams, accountants and B2B invoicing systems use the SIRET to confirm a supplier’s establishment is real and well-formed. This free validator runs the official Luhn check in your browser.
How it works
The SIRET uses the Luhn (mod-10) algorithm over all 14 digits:
- Strip spaces; you must have exactly 14 digits.
- Starting from the rightmost digit and moving left, double every second digit.
- If a doubled value exceeds 9, subtract 9 (equivalent to adding its two digits).
- Sum all the resulting values.
- The SIRET is valid if that sum is divisible by 10.
The first 9 digits are the SIREN (the parent company); the last 5 are the NIC establishment number. The NIC’s final digit is itself a Luhn check over the establishment, but practically the whole 14-digit Luhn test is what software verifies.
Special case: La Poste
La Poste establishments are the documented exception: their SIRETs are valid when the digit sum is divisible by 5, not via Luhn. This validator detects that pattern and reports it so a legitimate La Poste SIRET is not wrongly rejected.
Example
Check 73282932000074 → SIREN 732 829 320, NIC 00074. Apply Luhn from the right (double the 2nd, 4th, 6th… digits, subtract 9 where needed), sum the values, and confirm the total is divisible by 10. A passing result means the number is internally consistent — confirm the establishment is active in the INSEE Sirene database. Everything runs locally.