How is an ACN check digit calculated?

Multiply the first 8 digits by the weights 8,7,6,5,4,3,2,1, sum the products, take the remainder modulo 10, then compute 10 minus that remainder modulo 10. That value must equal the 9th (check) digit.

How many digits is an ACN?

An ACN is exactly 9 digits, usually displayed in three groups of three (e.g. 004 085 616). The tool ignores spaces so either format works.

What is the difference between an ACN and an ABN?

An ACN is a 9-digit identifier ASIC issues only to companies. An ABN is 11 digits and is issued to all business types. For most companies the last 9 digits of the ABN equal the ACN.

Does a valid check digit mean the company exists?

No. A valid check digit only confirms the number is internally consistent. To confirm a company is registered and current, search the official ASIC register. This tool performs no lookup.

Why does my ACN fail validation?

A failed check almost always means a digit was mistyped or transposed. Re-check all 9 digits against the source document, since a single wrong digit breaks the mod-10 test.

Australia ACN Validator

An Australian Company Number (ACN) is the unique 9-digit identifier the Australian Securities and Investments Commission (ASIC) issues to every company registered in Australia. Before relying on an ACN in a contract, onboarding flow or compliance check, you can confirm it is well-formed using ASIC’s check-digit algorithm. This validator runs that check entirely in your browser.

How it works

ASIC defines a weighted modulus-10 check digit over the first 8 digits, validated against the 9th:

Strip spaces so you have 9 digits.
Multiply the first 8 digits by the weights 8, 7, 6, 5, 4, 3, 2, 1.
Sum the products.
Take the remainder of that sum modulo 10.
Compute the complement: (10 - remainder) mod 10.
The ACN is valid if that complement equals the 9th digit.

Example

Validate 004 085 616 → digits 0 0 4 0 8 5 6 1 then check digit 6.

(0×8) + (0×7) + (4×6) + (0×5) + (8×4) + (5×3) + (6×2) + (1×1) = 84.

84 mod 10 = 4. Complement = (10 − 4) mod 10 = 6, which equals the 9th digit, so the ACN is valid.

Notes

A valid check digit confirms the number is well-formed, not that the company is currently registered. Search the official ASIC register to confirm status. Everything runs locally — your ACN never leaves your device.