An Australian Business Number (ABN) is a single identifier for all business dealings with the tax office and for dealings with other government departments and agencies.

You can use the form below to test if a ABN is valid.

If you don't have a ABN, you can use the following number to test the system: ABN

The verification algorithm embedded in the Australian Business Number
is known as a *check digit algorithm*: one of the digits (the
first two in this case) depends upon the others, meaning that if one
digit is changed, the last digit will not be correct anymore.

The general procedure is as follows: firstly, subtract 1 from the first
digit of the Australian Business Number of interest (our example
number 53 004 085 616 becomes 43 004 085 616). Each digit of the new
number is multiplied by a given *weight* (different weights are
used for the different digits), and the sum of these products should
be a multiple of 89. If it is not the case, there is an error in your
number.

Here is a complete example for the number 53 004 085 616. As we said, we substract 1 from the first number on the left, which gives us 43 004 085 616. We multiply each digit of this new number by the weights given below:

4 | 3 | 0 | 0 | 4 | 0 | 8 | 5 | 6 | 1 | 6 | ||||||||||||

x | x | x | x | x | x | x | x | x | x | x | ||||||||||||

10 | 1 | 3 | 5 | 7 | 9 | 11 | 13 | 15 | 17 | 19 | ||||||||||||

= | = | = | = | = | = | = | = | = | = | = | ||||||||||||

40 | + | 3 | + | 0 | + | 0 | + | 28 | + | 0 | + | 88 | + | 65 | + | 90 | + | 17 | + | 114 | = | 445 |

We then calculate the sum 40 + 3 + 0 + 0 + 28 + 0 + 88 + 65 + 90 + 17 + 114 = 445. Since 445 = 89 * 5, it is a multiple of 89, hence the number is valid.

References:

- Format of the Australian Business Number (ABN), on the ATO website.

Last modified: Thu Dec 11 19:12:00 EST 2003