ACN Validator
Check an Australian Company Number and see the company ABN it implies
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How the ACN check digit works
Take the first eight digits and multiply them by 8, 7, 6, 5, 4, 3, 2 and 1 in order. Add the results, take the remainder modulo 10, and subtract it from 10 (a remainder of zero gives a check digit of zero). That final value is the ninth digit. It catches every single mistyped digit and nearly every swapped pair, which covers most of the ways an ACN arrives wrong after being read off a printed invoice.
There is one blind spot, and it is a property of the algorithm rather than of this tool: swapping the last two digits sometimes lands on another number that also passes. If the ACN matters, check it against ASIC's register rather than relying on arithmetic alone.
From an ACN to the company ABN
An Australian company's ABN is its ACN with two digits in front, and those two digits are not arbitrary. They are the value that makes the ABN's own modulus 89 checksum come out even, which means the ACN determines the ABN exactly. This tool works that out and shows it, so you can move between the two numbers on a supplier record without a lookup. The reverse trip lives in the ABN validator, which reads the ACN out of an eleven digit number.
What a valid ACN does not tell you
Nothing about the company. Whether it is registered, still trading, in liquidation or has ever existed are all questions for ASIC's company register, which is the authoritative source and is free to search. A check digit only says the digits are internally consistent, and about one in ten random nine digit numbers is consistent by chance.
Storing ACNs
Store the nine digits as text, never as a number, or 000 000 019 becomes 19 the first time it round-trips through a spreadsheet. Display them grouped in threes the way ASIC does. Strip spaces before validating, and accept input pasted with the letters ACN in front, because that is how people copy them. Need sample values? The ACN generator makes them in batches.
Frequently Asked Questions
How do I work out an ACN check digit by hand?
Multiply the first eight digits by 8, 7, 6, 5, 4, 3, 2 and 1, add the results and take the remainder after dividing by 10. Subtract that remainder from 10, and a remainder of zero means a check digit of zero. The answer is the ninth digit of the ACN.
Can I get a company ABN from its ACN?
Yes, exactly. An Australian company ABN is its nine digit ACN with two extra digits in front, and those two digits are the only pair that makes the ABN checksum work. That means the ACN determines the ABN with no lookup required, which is what this tool shows alongside a valid result.
Why does an ACN start with zeros?
Because they were issued in sequence and the earliest companies got the lowest numbers. 000 000 019 is a real shape for an ACN. Store them as text: any system that treats an ACN as an integer will drop those zeros and produce a number that no longer validates.
Does a valid ACN mean the company is registered?
No. The check digit is arithmetic on the digits themselves and says nothing about the company. ASIC publishes a free company register, which is where questions about registration, status, deregistration and directors are actually answered.