Australia ACN validator
How the ACN format works
- Format
- 9-digit Australian Company Number (weighted mod-10 check digit)
- Example
- 004085616
Things to watch for
- 9 digits with its own weighted mod-10 checksum — different weights and modulus from the 11-digit ABN
- Every Australian company has an ACN, and most also derive an ABN by prefixing two check digits — don't confuse the two formats
- Checksum only — use ASIC's registers to confirm the company is actually registered
^[0-9]{9}$An ACN (Australian Company Number) is the 9-digit number ASIC assigns to a company the moment it’s incorporated in Australia — the identifier tied specifically to that corporate registration, distinct from any tax number the company might separately hold. It has to appear on a company’s official documents, from invoices to its common seal, wherever the company’s name is used in a formal capacity.
A weighted checksum, not a simple one
The ninth digit isn’t an arbitrary add-on — it’s derived from the first eight using a fixed set of weights (8 through 1, applied in order), summed and then subtracted from 10 to get the expected check digit. That’s a different calculation from the 11-digit ABN’s own mod-89 checksum, so an ACN and an ABN aren’t interchangeable just because a company happens to hold both.
How an ACN relates to an ABN
Most incorporated companies also register for an ABN, and when they do, that ABN is typically built by adding two extra check digits in front of the existing 9-digit ACN. But the reverse isn’t true — plenty of ABN holders (sole traders, trusts, partnerships) have never been incorporated and so have no ACN at all. The two numbers serve different registries for different purposes, even where one is embedded in the other.
What this check doesn’t confirm
A pass here means the 9 digits satisfy ASIC’s weighted checksum formula — nothing about whether that ACN was actually issued, or whether the company behind it is still registered and in good standing. For that, ASIC’s own registers (or the linked ABN Lookup service) are the authoritative source.
Content last reviewed 2026-07-22.
ACN FAQ
What's the difference between an ACN and an ABN?
ASIC issues an ACN to every company the moment it's incorporated — it's tied to corporate registration specifically. An ABN is a broader tax-registration number that sole traders, partnerships, and trusts can hold even without a company or an ACN; when a company does register for an ABN, that ABN is usually its own 9-digit ACN with two extra digits added at the front.
How is the ACN check digit calculated?
The first 8 digits are each multiplied by a fixed weight — 8, 7, 6, 5, 4, 3, 2, 1 in order — and the results are summed. That sum's remainder when divided by 10 is subtracted from 10 (treating a remainder of 0 as 0), and the result must equal the ninth digit. A single mistyped digit almost always breaks that equation.
Where does an ACN have to appear?
Australian law requires a company to print its ACN on public documents such as invoices, official correspondence, and its common seal, usually alongside its name. This tool only checks that a given 9-digit number is arithmetically valid — it doesn't confirm ASIC actually issued it to the company that's supposed to be showing it.