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:

1. Subtract 1 from the first (left) digit to give a new eleven digit number
2. Multiply each of the digits in this new number by its weighting factor
3. Sum the resulting 11 products
4. Divide the total by 89, noting the remainder
5. If the remainder is zero the number is valid

Weight factors (for Step 2)

Digit Position

1

2

3

4

5

6

7

8

9

10

11

Weight

10

1

3

5

7

9

11

13

15

17

19

Example

To check the validity of ABN 53 004 085 616

5

3

0

0

4

0

8

5

6

1

6

1. Subtract 1 from first (left) digit to give new number

4

3

0

0

4

0

8

5

6

1

6

2. Apply weighting factor

10

1

3

5

7

9

11

13

15

17

19

(4x10)+(3x1)+(0x3)+(0x5)+(4x7)+(0x9)+(8x11)+(5x13)+(6x15)+(1x17)+ (6x19)

3. 40+3+0+0+28+0+88+65+90+17+114
4. 445/89 = 5 remainder 0

The remainder is zero so the number is valid.

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Last Modified: Wednesday, 27 May 2009