Check Digit
As is the case with many identification numbers, the TFN includes a check digit for detecting erroneous numbers. The algorithm is based on simple modulo 11 arithmetic per many other digit checksum schemes. The weighting digits of the algorithm have been kept secret within the Australian Taxation Office since its creation, despite being communicated to more than 20,000 external entities in Australia, such as employers, investment bodies and software makers.
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 2 | ||||||||||
| x | x | x | x | x | x | x | x | x | ||||||||||
| 1 | 4 | 3 | 7 | 5 | 8 | 6 | 9 | 10 | ||||||||||
| = | = | = | = | = | = | = | = | = | ||||||||||
| 1 | + | 8 | + | 9 | + | 28 | + | 25 | + | 48 | + | 42 | + | 72 | + | 20 | = | 253 |
We then calculate the sum 1 + 8 + 9 + 28 + 25 + 48 + 42 + 72 + 20 = 253. Since 253 = 11 * 23, it is a multiple of 11, hence the number is valid.
Read more about this topic: Tax File Number
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