International · Validation
German Steuer-ID validator.
Check a German Steueridentifikationsnummer (the 11-digit personal tax ID) against its format rules and its MOD 11,10 check digit (Prüfziffer). It is not the Steuernummer or the USt-IdNr. It checks format and checksum only and cannot confirm a number was issued to anyone. Everything runs in your browser.
How it works: the ID has 11 digits, the first is not 0, and among the first ten exactly one digit appears two or three times while all others appear once. The 11th digit is an ISO/IEC 7064 MOD 11,10 check digit over the first ten.
Inputs
Result
Enter a Steuer-ID and press Check.
How a German Steuer-ID is built
The Steueridentifikationsnummer (IdNr, "Steuer-ID") is the lifelong 11-digit tax ID issued to every person in Germany. It is not the Steuernummer (the tax-office file number) and not the USt-IdNr (the VAT ID, checked in the EU VAT Number Validator).
| Rule | Detail |
|---|---|
| Length | 11 digits |
| First digit | Not 0 (leading 0 is reserved for test IDs) |
| Repeat rule | In the first 10 digits exactly one digit appears 2 or 3 times; every other digit appears once |
| Triple digits | If a digit appears 3 times, the three copies are never all next to each other |
| Digit 11 | Check digit (Prüfziffer), ISO/IEC 7064 MOD 11,10 over digits 1 to 10 |
MOD 11,10: start with a running product of 10. For each of the first ten digits, add the digit to the product and take the result mod 10 (a result of 0 counts as 10); the new product is that sum times 2, mod 11. The check digit is 11 minus the final product, and 10 becomes 0.
Checksum and format only, not a lookup
A passing result means the number is internally consistent. It cannot confirm the number was issued or belongs to anyone; only the Bundeszentralamt für Steuern holds that. Nothing is looked up.
Sources
Rules, repeat and triple-digit conditions, reference algorithm and example IDs: Bayerisches Landesamt für Steuern, Prüfung der Steuer- und Steueridentifikationsnummer (ELSTER). Structure and MOD 11,10 description (citing BZSt): Wikipedia: Steuerliche Identifikationsnummer. Independent implementation and test numbers: python-stdnum, stdnum/de/idnr.py. Check-character system: ISO/IEC 7064:2003.
Format and checksum only — not a register lookup
This tool checks the number entirely in your browser. It does not query the Bundeszentralamt für Steuern, and a valid result is not proof the number was ever issued or belongs to anyone. Nothing you type is transmitted, stored, or logged.