Austrian UID / ATU Validator
Official validator for Austrian UID / ATU with checksum verification and mathematical integrity.
About Austrian UID / ATU
The Umsatzsteuer-Identifikationsnummer (UID), characterized by the prefix ATU, is the Austrian Value Added Tax (VAT) identification number for businesses.
It is mandatory for cross-border EU trade (VIES validation), electronic invoicing, and domestic corporate billing.
Austrian UID / ATU Anatomy
The Austrian VAT number comprises the fixed prefix ATU and 8 numeric digits:
| Position | Field | Length | Meaning & Rule | Example |
|---|---|---|---|---|
| 1 to 3 | Prefix | 3 chars | Fixed ATU (Austria VAT) | ATU |
| 4 to 10 | Company Serial | 7 digits | Registration sequence with the Federal Ministry of Finance | 1234567 |
| 11 | Check Digit | 1 digit | Calculated using modified Luhn algorithm with +4 constant | 5 |
Official Austrian ATU Algorithm
Corporate validation rule from the Austrian Federal Ministry of Finance (BMF):
Sum = OddSum(0,2,4,6) + CrossSum(Even(1,3,5)*2) + 4; CheckDigit = (10 - (Sum mod 10)) mod 10.
- 1. Take the 7 numeric digits following ATU.
- 2. Sum the digits in odd positions (indices 0, 2, 4, 6).
- 3. Multiply digits in even positions (indices 1, 3, 5) by 2 and add their digital sum if >= 10.
- 4. Add the constant +4 to the accumulated total.
- 5. The final check digit is (10 - (Sum mod 10)) mod 10, which must match the 8th digit.