Australia TFN Validator
Online validator for Tax File Number (TFN) issued by the Australian Taxation Office (ATO).
How does TFN validation work?
The validator checks for 9 numeric digits and executes the official ATO Modulo 11 weighted sum check.
If the weighted sum is congruent to zero modulo 11, the TFN is structurally valid. All validation runs securely in your browser.
TFN Calculation and Validation Algorithm (Weighted Modulo 11)
The official Australian Taxation Office (ATO) algorithm applies positional weights and modulo 11 division:
Sum = d₁ × 1 + d₂ × 4 + d₃ × 3 + d₄ × 7 + d₅ × 5 + d₆ × 8 + d₇ × 6 + d₈ × 9 + d₉ × 10; Valid if Sum mod 11 = 0
- Extract all 9 digits of the TFN.
- Multiply each digit by its corresponding positional weight [1, 4, 3, 7, 5, 8, 6, 9, 10].
- Sum all 9 resulting products together.
- The TFN is mathematically valid if the total sum is an exact multiple of 11 (remainder 0).