Australia ABN Validator
Online validator for Australian Business Number (ABN) issued by the Australian Taxation Office (ATO).
How does ABN validation work?
The validator verifies that the input consists of 11 numeric digits and applies the ATO Modulo 89 linear congruence check.
Validation occurs in real time within your browser with complete privacy and without calling external servers.
ABN Calculation and Validation Algorithm (Weighted Modulo 89)
The official Australian Taxation Office (ATO) algorithm applies positional weights and modulo 89 division:
Sum = (d₁ - 1) × 10 + d₂ × 1 + d₃ × 3 + d₄ × 5 + d₅ × 7 + d₆ × 9 + d₇ × 11 + d₈ × 13 + d₉ × 15 + d₁₀ × 17 + d₁₁ × 19; Valid if Sum mod 89 = 0
- Subtract 1 from the first digit of the 11-digit number.
- Multiply each digit by its respective weight [10, 1, 3, 5, 7, 9, 11, 13, 15, 17, 19].
- Sum all resulting products together.
- The ABN is mathematically valid if the total sum is divisible by 89 with zero remainder.