ABN Validator
Validate an ABN (Australian Business Number) — the 11-digit identifier issued by the Australian Business Register. The ABN uses a single mod-89 checksum over a weighted sum: subtract 1 from the first digit, weight all eleven digits by [10,1,3,5,7,9,11,13,15,17,19], sum, and the result must be a multiple of 89. See the full weighted breakdown. Everything runs locally in your browser.
Validate an ABN
ABN structure: 11 digits (spaces are tolerated on input and stripped). The check is a whole-number mod-89 sum, not a single appended check digit, so an ABN can't be built from a free prefix the way a Luhn/CUSIP code can — they are issued. The algorithm: take the 11 digits, subtract 1 from the first (leftmost) digit, multiply each by the fixed weights 10, 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, sum the products, and the ABN is valid iff that sum is divisible by 89. An ABN's last nine digits embed the entity's ACN (Australian Company Number) for companies. Pairs with the IBAN, ISIN, SEDOL and CUSIP validators. Everything runs locally — nothing leaves your browser.