SIREN, SIRET and VAT: three numbers for one company
The SIREN has 9 digits. INSEE, the French statistics office, assigns it to every company when it joins the Sirene register, and it never changes. The SIRET has 14 digits: the SIREN followed by a 5-digit number for each establishment, the NIC. The French EU VAT number is FR, then a 2-digit key, then the SIREN.
| Number | Format | Example (La Poste) |
|---|---|---|
| SIREN | 9 digits | 356 000 000 |
| SIRET | SIREN + 5 digits | 356 000 000 00048 |
| EU VAT number | FR + key + SIREN | FR39356000000 |
How the tool checks a number
- The check digit. The last digit of a SIREN or SIRET is computed from the others with the Luhn algorithm, so a one-digit typo is caught. La Poste’s establishments follow a rule of their own, which the tool knows.
- The VAT key. It is (12 + 3 × (SIREN mod 97)) mod 97. For 356 000 000, the remainder of the division by 97 is 9, and (12 + 27) mod 97 gives 39.
- The company directory. The tool queries the French government’s public API, built on INSEE’s Sirene register, to show the company’s name, address, NAF activity code and status.
- VIES. The European Commission’s service says whether the VAT number is active, today, in the country that issued it. It also accepts numbers from the other EU countries.
Why check before you invoice
Under the French e-invoicing reform, the customer’s SIREN becomes a mandatory mention on invoices between businesses. It is also what your accredited platform uses to find the customer’s platform in the directory. One wrong digit, and the invoice can be rejected.
For a sale to a business in another EU country without French VAT, the invoice shows the customer’s VAT number. Checking it in VIES at the time of the sale, and keeping the date of that check, helps you show that you did.
Frequently asked questions
How do you get the French VAT number from a SIREN?
A French VAT number is FR, then a two-digit key, then the 9-digit SIREN. The key is (12 + 3 × (SIREN mod 97)) mod 97, with a leading zero if it has one digit. For the SIREN 356 000 000, the key is 39, so the VAT number is FR39356000000.
What is the difference between a SIREN and a SIRET?
The SIREN identifies the company and has 9 digits. The SIRET identifies each of its establishments and has 14 digits: the SIREN followed by a 5-digit internal number, the NIC. A company has one SIREN and as many SIRET numbers as it has establishments.
Does a valid SIREN prove the company exists?
No. The check digit catches typos, not made-up numbers. That’s why the tool also looks the number up in the official company directory, which tells you whether the SIREN has been assigned and whether the company is still active.
Why is a VAT number shown as inactive in VIES?
Most often the company has no active VAT number: a French micro-entrepreneur under the VAT exemption threshold, a closed company, or a registration too recent to appear in VIES yet. A country’s service can also be briefly unavailable. If in doubt, ask your customer for their number.
Do I need my customer’s SIREN on an invoice?
Under the French e-invoicing reform, the customer’s SIREN is one of four new mandatory mentions when the customer is a business. They apply from September 1, 2026 for large and mid-sized companies, and from September 1, 2027 for SMEs, very small businesses and micro-entrepreneurs.