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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.

Reviewed by the thecalcu.com team · Last updated 14 July 2026

🇦🇺This tool is specific to Australia

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.

Why Use an Australia ABN Validator?

A mistyped ABN on an invoice, a supplier record, or an accounting system entry can cause processing errors or compliance issues down the line, especially since many GST and tax-related processes depend on a correctly recorded ABN. Because the ABN format includes a checksum relationship across all 11 digits, most simple typos can be caught immediately rather than discovered later during a reconciliation or audit.

This validator gives that immediate check without needing to look the number up anywhere. A bookkeeper entering supplier ABNs into an accounting system, or a developer building an Australian invoicing tool, can validate format client-side before the number gets used further downstream.

Who Should Use This Validator?

  • Bookkeepers and accountants verifying ABN format before entering supplier or client records into accounting software.
  • Developers building Australian invoicing, e-commerce, or business registration tools who need client-side ABN format validation.
  • Small business owners double-checking their own ABN was entered correctly on invoices or registration forms.
  • Procurement and accounts payable teams spot-checking supplier ABNs before processing payments.
  • Anyone receiving an invoice from an Australian business who wants a quick format sanity check on the ABN shown.

What Insights Does the Australia ABN Validator Give You?

The validator checks two things about the number you enter:

  • Format, confirms the number is exactly 11 digits, the standard ABN length.
  • Checksum, verifies the ABR's specific weighted-sum algorithm confirms the number is correctly formed.

A passing result confirms the ABN is structurally correct according to the ABR's published algorithm, it does not confirm the number is actually registered or active, since that requires checking the official ABN Lookup tool.

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.
Show formula & methodology ↓Show less ↑

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

What is an Australian Business Number?
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.
How does this validator check an 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.
What is the ABN checksum formula?
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.
Does a valid checksum mean the ABN is active and registered?
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.
Can I enter my ABN with or without spaces?
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.
Is my ABN data stored or transmitted anywhere when I use this tool?
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.
Why would an ABN fail this validation check?
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.
What is the difference between an ABN and a TFN?
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.
Is an ABN the same as an Australian company number (ACN)?
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.
Where do I find a business's ABN?
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