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.
Anatomy & Structure of the ABN (Australian Business Number)
The Australian Business Number consists of 11 digits structured in 2 parts:
| Position | Field | Length | Meaning & Rule | Example |
|---|---|---|---|---|
| 1 & 2 | Weighted Check Digits | 2 digits | Integrity check digits calculated via Modulo 89 (with 1 subtracted from 1st digit) | 51 |
| 3 to 11 | ACN / Base Identifier | 9 digits | Matches the 9-digit Australian Company Number (ACN) or unique ATO sequence | 824753556 |
Official Algorithm (Weighted Modulo 89 — ATO)
Official check algorithm for Australian Business Number:
S = ((d[0] - 1) * 10) + Σ (d[i] * W[i]) (i=1..10); Valid if S mod 89 === 0
- 1. Subtract 1 from the first digit (position 1).
- 2. Multiply the 11 digits by weights: W = [10, 1, 3, 5, 7, 9, 11, 13, 15, 17, 19].
- 3. Sum all weighted products to get total S.
- 4. Compute remainder of S divided by 89.
- 5. The ABN is valid if and only if remainder is exactly zero (S mod 89 = 0).