ABN & ACN Validator
Instantly check whether an Australian Business Number (ABN) or Australian Company Number (ACN) is valid using the official check digit algorithm. Free, no sign-up required.
0/11 digits entered
About ABN & ACN Validation
ABN (Australian Business Number) is an 11-digit identifier issued by the Australian Business Register. The validation algorithm subtracts 1 from the first digit, multiplies each digit by its weight [10,1,3,5,7,9,11,13,15,17,19], and checks if the sum is divisible by 89. ACN (Australian Company Number) is a 9-digit identifier for companies registered with ASIC. The check digit is the complement of the weighted sum (weights 8-1) modulo 10. Important: A valid check digit only means the number is mathematically correct - it does not confirm the business exists or is currently active. Use the ABR lookup for that.
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How ABN Validation Works
Every ABN contains a built-in check digit that allows mathematical validation without needing to query an external database. The algorithm subtracts 1 from the first digit, multiplies each of the 11 digits by its corresponding weight (10, 1, 3, 5, 7, 9, 11, 13, 15, 17, 19), sums the products, and checks whether the total is evenly divisible by 89.
ACN validation is similar but uses 9 digits with weights 8 through 1. The check digit (the 9th digit) is calculated as the complement of the weighted sum modulo 10.
How to use this ABN validator
- Enter or paste the 11-digit ABN or 9-digit ACN into the input field. Spaces and formatting are handled automatically.
- The tool instantly checks the number against the official ATO check digit algorithm.
- Review the result - a green tick means the number is structurally valid; a red cross means there is a digit error or typo.
- For active status confirmation, follow the link to the Australian Business Register (ABR) lookup.
Why ABN validation matters for Australian businesses
Under Australian tax law, if a supplier does not quote a valid ABN on their invoice, the paying business is required to withhold 47% of the payment amount and remit it to the ATO. This no-ABN withholding rule catches many businesses off guard, particularly in construction, cleaning, and trade services where subcontractor invoices are common. Validating ABNs at the point of invoice receipt prevents costly withholding obligations and avoids disputes with suppliers who may not realise their ABN is incorrect.
- Before paying a contractor invoice - an invalid ABN means you must withhold 47% for tax.
- During supplier onboarding to catch typos before they enter your system.
- When verifying tax invoices meet GST requirements (a valid ABN is mandatory).
- For bulk data cleaning of your accounts payable master file.
Important note
This tool validates the mathematical structure of an ABN or ACN only. It does not confirm whether the number is currently active, cancelled, or associated with a specific entity. For that, use the official Australian Business Register (ABR) lookup at abr.business.gov.au.
How AP automation handles ABN validation
Manually checking ABNs on every supplier invoice is tedious and error-prone. Pulsify automatically validates supplier ABNs when invoices are received, flagging invalid or missing numbers before they reach your approval queue. This keeps your supplier master file clean and ensures you never accidentally trigger the 47% no-ABN withholding obligation.
See how Pulsify automates AP for growing businesses →Automate ABN validation in your AP workflow
Pulsify automatically validates supplier ABNs when invoices are received, flagging issues before they reach your approval queue.