Business Australia
ACN Validator (Australian Company Number)
An Australian Company Number is the nine-digit identifier ASIC gives every company, and its last digit is a check digit calculated from the others. This validator applies ASIC's rule, shows each step and works out what the last digit should be if yours is wrong.
Free, no signup Runs in your browser
Nine digits. Spaces are fine. Checked in your browser.
Result
—Formatted
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Weighted total
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Check digit should be
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Check digit found
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The working, digit by digit
How do I check if an ACN is valid?
Multiply the first eight digits by 8, 7, 6, 5, 4, 3, 2 and 1 and add them. The ninth digit must equal 10 minus the last digit of that total, counting 10 as 0. For 004 085 616 the total is 84, so the check digit is 6, which it is. A pass proves the number is well formed, not that the company exists.
What an ACN is
ASIC allocates an ACN when a company is registered, and it must appear on a company's public documents with its name. It is different from an ABN, which identifies the business to the tax system, though many companies have both and the two are linked.
Registered Australian bodies, such as some foreign companies, also receive an ARBN, which is nine digits with the same check rule.
What passing means
Passing shows the digits are consistent with the rule. It does not show the company is registered, current or the one you expect. Search ASIC's register or ABN Lookup to confirm. A failure usually means a typing error.
To check an 11-digit ABN, use the ABN validator.
How this is calculated
The rule, step by step, so you can check any figure by hand.
multiply the first eight digits by 8, 7, 6, 5, 4, 3, 2, 1 and add the resultscheck digit = (10 − the total's last digit), counting 10 as 0the ninth digit of the ACN must equal that check digit
The rule is modulus 10 with descending weights. It catches any single mistyped digit and most swapped neighbours, which is its job: stopping typing errors on forms and invoices. It does not prove anything about the company.
A company's ABN is usually built on its ACN, with the two ABN check digits placed in front, so a valid ACN is a good first test before searching ABN Lookup.
A worked example
The ACN 004 085 616.
- Weighted digits0×8 + 0×7 + 4×6 + 0×5 + 8×4 + 5×3 + 6×2 + 1×1 = 84
- Last digit of 844
- Check digit, 10 − 46
- Ninth digit of the ACN6, so it passes
A well-formed ACN.
Change any digit and it fails.
Privacy
The number is processed in your browser and goes nowhere. ACNs are public information in any case.
What it leaves out
It does not look up names, status or directors. ASIC's search does.
What this calculator does not do
- Nine-digit numbers only
- Shows the number is well formed, not that it is registered
- No lookup
- ABNs have their own validator
Common questions
How long is an ACN?
Nine digits.
How is the ACN check digit worked out?
Weight the first eight digits by 8 to 1, add them, and the check digit is 10 minus the last digit of the total.
Is an ACN the same as an ABN?
No. An ABN has 11 digits and identifies a business to the tax system.
Does a valid ACN mean the company exists?
No. Only ASIC's register confirms it.
What is an ARBN?
A nine-digit number for registered foreign companies, with the same check rule.
Where these numbers come from
- ASIC — Australian company number digit check How the ACN's ninth digit is derived
- ASIC — company search Where to confirm a company is registered
Method last reviewed 2026-10-28 This calculator uses fixed rules rather than rates that change, and its method is re-checked against the sources above at least once a year. Out of date? Tell us and we will fix it.
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