The Australian Business Number, or ABN, is a unique identifier issued by the Australian Business Register (ABR) which is operated by the Australian Taxation Office (ATO). The ABN is a component of the reform known as A New Tax System introduced by John Howard's Liberal government on 1 July 2000.
The ABN is an eleven digit number where the first two digits are a checksum. Unlike with the Tax File Number (TFN), the ATO has publicised the formula for checking and creating valid ABN checksums. Also, the nature of the ABN algorithm means that any 9-digit number can be made into a valid ABN.
In the case of companies, the ATO determines the ABN by using the company's Australian Company Number (ACN) to which is prefixed the two-digit checksum
Format of the Australian Business Number (ABN)
Confirm an ABN
The following formula can be used to verify the ABN you are allocated or to verify the ABN issued to a business you deal with.To verify an ABN:
- Subtract 1 from the first (left) digit to give a new eleven digit number
- Multiply each of the digits in this new number by its weighting factor
- Sum the resulting 11 products
- Divide the total by 89, noting the remainder
- If the remainder is zero the number is valid