Free tool · ABN & ACN check digits
Free bulk ABN and ACN validator
Paste a list of ABNs or ACNs and see in one second which ones are validly formed. Catches typos, transposed digits and made-up numbers before they reach your invoices or CRM.
Validator
Paste ABNs or ACNs, one per line
Spaces and dashes are fine. 11 digits are checked as an ABN, 9 digits as an ACN (or ARBN).
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The maths
How ABN and ACN check digits work
Every Australian Business Number has a built-in check. Subtract 1 from the first digit, multiply the 11 digits by the weights 10, 1, 3, 5, 7, 9, 11, 13, 15, 17 and 19, and add them up. If the total divides evenly by 89, the ABN is validly formed. A single mistyped digit or two swapped digits almost always breaks the rule, which is why a format check catches most data-entry errors.
An Australian Company Number uses a simpler rule. Multiply the first 8 digits by 8, 7, 6, 5, 4, 3, 2 and 1, add them, find the remainder after dividing by 10, and subtract it from 10 (10 becomes 0). The answer must match the 9th digit. A company's ABN is usually 2 digits followed by its ACN, so the validator also tells you when the last 9 digits of an ABN form a valid ACN.
What a format check can't tell you: whether the ABN is still active, who it belongs to, or whether the business is registered for GST. Those answers only come from the Australian Business Register. For a handful of numbers, use the free search at abr.business.gov.au. For a whole list, our bulk ABN lookup returns status, entity name, GST registration and location at US$2 per 1,000 matches.
FAQ
Frequently asked questions
Does a valid ABN mean the business is registered?
No. The check digit only proves the number is correctly formed, which catches typos and made-up numbers. To confirm an ABN is active and GST-registered you need the Australian Business Register, which our paid bulk ABN lookup does at US$2 per 1,000 matches.
How does the ABN check digit work?
Subtract 1 from the first digit, multiply each of the 11 digits by the weights 10, 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, add the results and divide by 89. A valid ABN leaves no remainder.
How does the ACN check work?
Multiply the first 8 digits by the weights 8 down to 1, add them, take the remainder after dividing by 10 and subtract it from 10 (a result of 10 becomes 0). That must equal the 9th digit.
Is my data uploaded anywhere?
No. The check runs entirely in your browser with JavaScript. Nothing you paste is sent to a server.
Is this tool free?
Yes, the validator is free with no sign-up. It was built with AI assistance by Luke Main.
Independent tool, not endorsed by or affiliated with the ABR, ATO, ASIC or the Australian Government. General information only.