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.
Anatomy & Structure of TFN (Tax File Number) — Australia
The Australian Tax File Number consists of 8 or 9 digits in 2 parts:
| Position | Field | Length | Meaning & Rule | Example |
|---|---|---|---|---|
| 1 to 8 | Base Tax Number | 8 digits | Unique tax identification sequence assigned by ATO | 12345678 |
| 9 | Check Digit | 1 digit | Calculated via weighted Modulo 11 with official ATO weights | 2 |
Official Algorithm (Weighted Modulo 11 — ATO)
Official validation algorithm for 9-digit Australian TFN:
S = Σ d[i] * W[i] (i=0..8); Valid if S mod 11 === 0
- 1. Multiply the 9 digits by official ATO weights: W = [1, 4, 3, 7, 5, 8, 6, 9, 10].
- 2. Sum all products into total S.
- 3. Compute remainder of S divided by 11.
- 4. The TFN is valid if and only if S mod 11 equals exactly 0.