Austrian VAT Number Validation

Austrian VAT numbers (Umsatzsteuer-Identifikationsnummer or UID-Nummer) are issued by the Finanzamt (tax office) and always begin with the letter U followed by 8 digits.

Format Overview

Regex Pattern

^ATU[0-9]{8}$

Or without country prefix:

^U[0-9]{8}$

Checksum Algorithm

Austrian VAT numbers use a custom weighted algorithm similar to Luhn:

1. Process the first 7 digits with alternating weights
2. For even positions: floor(digit/5) + (2 * digit) % 10
3. Sum all weighted values and add 4
4. Check digit = (10 - sum % 10) % 10

def validate_at_vat(number):
    # Remove ATU prefix if present
    if number.startswith('ATU'):
        number = number[3:]
    if number.startswith('U'):
        number = number[1:]

    if len(number) != 8 or not number.isdigit():
        return False

    # Calculate checksum
    total = 0
    for i, digit in enumerate(number[:7]):
        d = int(digit)
        if i % 2 == 0:  # Even position (0-indexed)
            d = d // 5 + (2 * d) % 10
        total += d

    total += 4
    check = (10 - total % 10) % 10

    return check == int(number[7])