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Australia ABN Validator

Finance & Global IDs

Validate an Australian Business Number (ABN) using the official checksum algorithm. Check any 11-digit ABN instantly, entirely in your browser.

What is a Australia ABN?

An Australia ABN Validator checks whether an Australian Business Number follows the correct structural format the Australian Business Register (ABR) uses when issuing these numbers — an 11-digit number with a specific weighted checksum that catches the overwhelming majority of typos and invalid numbers immediately. ABNs appear on virtually every Australian business invoice and official document, making a quick format check useful before relying on a number in an important context.

This validator applies the ABR's official checksum algorithm directly, telling you immediately whether a number is correctly formed. For the equivalent personal tax identifier, see the Australia TFN Validator, and for comparable business tax identifiers elsewhere, see the GST Validator and VAT Number Validator.

How to use this Australia ABN calculator

  1. Enter the Australian Business Number in the Australian Business Number field, with or without spaces.
  2. Read the result card to see whether the number passed validation.
  3. If it failed, check the details breakdown to see the calculated checksum value.
  4. Compare the number against the business's official invoice or registration documentation to find the discrepancy.
  5. For confirming active registration status (not just format), search the official ABN Lookup tool separately.

Formula & Methodology

An ABN is validated using a weighted modulo-89 checksum:

1. Subtract 1 from the first (leftmost) digit.
2. Multiply each of the 11 digits by its corresponding weight: 10, 1, 3, 5, 7, 9, 11, 13, 15, 17, 19.
3. Sum all eleven weighted products.
4. The ABN is valid if this sum is evenly divisible by 89.

Worked example: for the ABN 51 824 753 556 (51824753556):
- After subtracting 1 from the first digit: 41824753556
- Weighted sum of all 11 digits = 534
- 534 ÷ 89 = 6 exactly, so the checksum passes.

Frequently Asked Questions

An Australian Business Number (ABN) is an 11-digit identifier issued by the Australian Business Register (ABR) to businesses and other organisations, used for GST registration, invoicing, and dealings with government and other businesses. Most invoices issued in Australia are required to display a valid ABN.
The validator confirms the number is exactly 11 digits, then applies the Australian Business Register's official checksum algorithm — subtracting 1 from the first digit, multiplying each digit by a specific weight, summing the results, and checking that the total is evenly divisible by 89.
First subtract 1 from the leftmost digit. Then multiply all 11 digits by their corresponding weights (10, 1, 3, 5, 7, 9, 11, 13, 15, 17, 19), sum the products, and the ABN is valid if that sum is exactly divisible by 89. This specific algorithm is published directly by the Australian Business Register.
No — a passing checksum only confirms the number is structurally well-formed according to the ABR's algorithm, not that it's currently registered, active, or belongs to a real business. To confirm an ABN's actual registration status, search the official ABN Lookup tool on the Australian Business Register website.
Yes — ABNs are commonly displayed in a grouped format (like 51 824 753 556), and this validator accepts that format as well as a continuous 11-digit string, stripping spaces automatically before checking.
No — the entire validation runs locally in your browser using JavaScript. The ABN you enter is never sent to a server, logged, or stored anywhere.
The most common reasons are a mistyped digit, a missing or extra digit, or a number that was never a real ABN to begin with — such as a placeholder number used on a template invoice. Double-check the number against the business's official documentation or registration certificate.
An ABN identifies a business or organisation for GST, invoicing, and business-level tax purposes, while a TFN (Tax File Number) identifies an individual or entity for personal or entity-level tax administration. Use the [Australia TFN Validator](/australia-tfn-validator/) for checking tax file numbers instead.
No — an ACN (Australian Company Number) is a separate 9-digit identifier issued specifically to companies by ASIC, while an ABN is an 11-digit number issued more broadly to businesses, sole traders, and other entities by the ABR. A registered company's ABN often (but not always) embeds its ACN within the number.
ABNs are typically printed on invoices, business registration documents, and official correspondence from a business. You can also search for a specific business's ABN using the free ABN Lookup tool on the Australian Business Register's official website.
Also known as
ABN checkerAustralian business number validatorABN checksumverify ABNbusiness number lookup format