ACN, ABN, ARBN and ARSN explained

Australian businesses carry several look-alike identifiers. An Australian Company Number (ACN) is the nine-digit number ASIC gives every company at registration. An Australian Business Number (ABN) is an eleven-digit number issued by the Australian Business Register for tax and invoicing, and for a company it usually contains the ACN. An Australian Registered Body Number (ARBN) is the ACN equivalent for foreign companies and registered Australian bodies, and an Australian Registered Scheme Number (ARSN) identifies a managed investment scheme. All four are accepted by asicapi wherever a company id is expected.

The four identifiers side by side

ASIC's own register knows the first three; the ABN is added from a feed the Australian Business Register sends to ASIC, which is why abn can be null for a company that never applied for one.

When to use which

• To look up a company on the ASIC register, use the ACN. It is the primary key of the register and never changes, even when the company changes its name.
• If you only have an ABN, you can still call GET /v1/companies/{id} with it. asicapi validates the ABN, extracts the embedded ACN and resolves the company. This only works for ACN-based ABNs; a sole trader's or trust's ABN has no ACN inside it and returns abn_not_acn_based.
• Foreign companies and registered Australian bodies have no ACN. Use the ARBN. Their record shows numberType.code of ARBN.
• Managed investment schemes are identified by ARSN, numberType.code of ARSN.
• Business names have none of these. They are identified by a state registration number or ASIC identifier and served from /v1/business-names.

The numberType object on every company tells you which kind of number acn holds:

Code NUMBER ("Registration number") appears on records such as trusts and non-registered entities where ASIC allocated an internal number that is not an ACN, ARBN or ARSN.

The ACN check digit algorithm

The ninth digit of an ACN is a check digit computed from the first eight. ASIC publishes the algorithm, and asicapi applies it before sending any request to ASIC so a typo fails fast with acn_invalid rather than a slower company_not_found.

ARBNs and ARSNs use exactly the same construction, so one validator covers all three.

Valid ACNs for testing

These ACNs all pass the check digit test and are published by ASIC for exactly this purpose. The sandbox accepts any of them; company 009 136 109 is ASIC's public sample company and is the only one with document images available in the sandbox.

The ABN check and the embedded ACN

An ABN has its own checksum, defined by the Australian Business Register:

1. Subtract 1 from the first digit.
2. Multiply the eleven digits by the weights 10, 1, 3, 5, 7, 9, 11, 13, 15, 17, 19.
3. Sum the products. The ABN is valid if the sum is divisible by 89.

For ABN 53 004 085 616, the first digit becomes 4. The products are 40, 3, 0, 0, 28, 0, 88, 65, 90, 17 and 114, which sum to 445. 445 divided by 89 is exactly 5, so the ABN is valid.

When a company applies for an ABN, the Registrar forms it by prefixing the company's ACN with two check digits. The last nine digits of 53 004 085 616 are 004 085 616, which is the ACN. asicapi returns this as acnFromAbn and uses it to resolve companies by ABN. If the extracted nine digits do not themselves pass the ACN check, the ABN is treated as not ACN based.

Validating identifiers with the API

GET /v1/identifiers/{value} detects the type of any identifier, checks it and returns normalised and display forms. It never contacts ASIC and is free.

curl https://api.asicapi.dev/v1/identifiers/53%20004%20085%20616 \
  -H "Authorization: Bearer $ASICAPI_KEY"

{
  "object": "identifier",
  "input": "53 004 085 616",
  "type": "abn",
  "valid": true,
  "normalized": "53004085616",
  "formatted": "53 004 085 616",
  "acnFromAbn": "004085616"
}

Because ACNs, ARBNs and ARSNs are indistinguishable by format alone, a nine-digit input that passes the check is reported as "type": "acn". The register tells you what it really is: read numberType on the company record. A value that is neither nine nor eleven digits, or that fails its checksum, comes back with "type": "unknown" or "valid": false respectively.

Related errors

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