🔒 The checksum runs entirely in your browser.
A valid checksum means the number is well-formed, not that the business exists or is currently registered. For that, check the official Australian Business Register. This is general information, not legal or financial advice.
Using an AI agent or a script? Call this tool as an API
AI agents and scripts can call this tool directly, to check their work or look something up, and get JSON back with the same answer this page gives. No key needed.
GET https://digitalgreenhouse.com.au/api/tools/abn-validator?number=51824753556number— string, required. The ABN or ACN. Also accepted asabn,acn.
The API answers from our server, and our code doesn’t store what you send. Fair-use limits apply. API guide · all endpoints (JSON) · OpenAPI
How ABN and ACN validation works
Both numbers have a built-in check digit so software can spot a typo without contacting any database. An ABN is 11 digits: subtract 1 from the first digit, multiply each digit by a fixed set of weights, add them up, and a genuine ABN divides evenly by 89. An ACN is 9 digits, where the last digit is a checksum of the first eight. This tool runs those exact calculations.
It’s a genuinely useful first line of defence: a mistyped ABN on an invoice, or a made-up one on a dodgy quote, will usually fail the checksum immediately. A number that passes still needs to be confirmed against the live register — we link you straight there.