Austrian Firmenbuchnummer
Validator
Check whether an Austrian Firmenbuchnummer (FN) is correctly formatted and passes the official BMJ check-letter algorithm — entirely in your browser.
About Austrian Firmenbuchnummer Validation
The Firmenbuchnummer is the official registration code for Austrian commercial companies (GmbH, AG), administered by the Federal Ministry of Justice (BMJ).
Formatted as 'FN XXXXXX y' — up to six digits (left-padded with zeros if fewer) plus a lowercase check letter.
Anatomy of Austrian Firmenbuchnummer
| Position | Field | Length | Meaning & Rule | Example |
|---|---|---|---|---|
| 1 to 3 | Optional Prefix | 3 characters | Prefix 'FN' indicating commercial register | FN |
| 4 to 9 | Sequential Number | 1 to 6 digits | Sequential registration number in commercial court | 575737 |
| 10 | Check Letter | 1 letter | Lowercase check letter from the BMJ lookup table | y |
Official Modulo 17 Algorithm
| Step | Description |
|---|---|
| 1. Weight each digit | Multiply the six digits (left-padded with zeros if fewer than six) by the fixed weights 6, 4, 14, 15, 10, 1, in that order. |
| 2. Sum the weighted products | Add all six weighted products together. |
| 3. Reduce modulo 17 | Calculate the remainder of the sum divided by 17 (Sum % 17). |
| 4. Look up the check letter | Use the remainder (0 to 16) as an index into the 17-letter table a, b, d, f, g, h, i, k, m, p, s, t, v, w, x, y, z and compare it to the given check letter. |
Frequently Asked Questions
What is the difference between FN and UID?
FN (Firmenbuchnummer) is the company's registration number in Austria's commercial register (Firmenbuch), administered by the Federal Ministry of Justice. UID (Umsatzsteuer-Identifikationsnummer) is the separate Austrian VAT number, administered by the tax authority. A company has both, independently of each other.
Is the "FN" prefix mandatory?
The underlying number and check letter are what matter for validation — "FN" is a conventional display label commonly shown on official documents and the business register, but systems and forms may store or accept just the digits and check letter without it.
Are the generated numbers official or real?
No. This validator only checks the format and Modulo 17 checksum — it does not look up any real company in the Firmenbuch register. A result of "valid" means the number is mathematically well-formed, not that it belongs to a real registered company.