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TFN

Tax

Australia Tax File Number

A unique 9-digit number issued by the Australian Taxation Office (ATO) to individuals and entities for tax administration, required for employment, banking, and tax filing.

Definition

A Tax File Number (TFN) is a unique nine-digit number issued by the Australian Taxation Office (ATO) to individuals and entities for tax administration. It's required for nearly every formal financial and employment interaction in Australia — from starting a new job to opening a bank account or filing a tax return.

Like several other national tax identifiers, a TFN includes a built-in checksum, which lets systems catch many typos before a submission is ever processed by the ATO. The Australia TFN Validator applies this checksum directly.

Formula

The TFN checksum uses a weighted modulo-11 calculation:

  1. Multiply each of the 9 digits by its corresponding weight: 1, 4, 3, 7, 5, 8, 6, 9, 10.
  2. Sum all nine weighted products.
  3. The TFN is valid if this sum is evenly divisible by 11.

Worked Example

For the TFN 123 456 782 (123456782):

Weighted products: (1×1) + (2×4) + (3×3) + (4×7) + (5×5) + (6×8) + (7×6) + (8×9) + (2×10) = 1 + 8 + 9 + 28 + 25 + 48 + 42 + 72 + 20 = 253

253 ÷ 11 = 23 exactly, so the checksum passes, confirming the TFN is correctly formed.

Key Things to Know

  • 9 digits, weighted checksum: the standard individual TFN format uses weights 1, 4, 3, 7, 5, 8, 6, 9, 10 with a divisible-by-11 rule.
  • Required to avoid maximum tax withholding: without a TFN on file, employers and banks must withhold tax at the top marginal rate.
  • Distinct from ABN: a TFN is a personal/entity tax identifier, while an ABN identifies a business specifically for GST and invoicing.
  • A valid checksum isn't proof of an active TFN: only the ATO can confirm whether a specific number is actually issued and active.

Related Terms

ABNAustralian Business NumberPANPermanent Account Number

Frequently Asked Questions

A TFN is required for employment, opening bank accounts, claiming government benefits, and filing tax returns in Australia. Without providing a TFN, employers and banks must withhold tax at the highest marginal rate on payments made to you.
Each of the 9 digits is multiplied by a specific weight (1, 4, 3, 7, 5, 8, 6, 9, 10 respectively), the products are summed, and the TFN is valid if that sum is exactly divisible by 11. This catches most single-digit typos and transposition errors.
No — a passing checksum only confirms the number is structurally well-formed according to the ATO's algorithm, not that it's been issued or belongs to a real person. Confirming an actual TFN requires official verification through the ATO.
Yes — an older 8-digit TFN format was historically issued to some non-individual entities, using a different checksum than the standard 9-digit format used for individuals today.
A TFN identifies an individual or entity for personal or entity-level tax purposes, while an [ABN](/glossary/abn/) specifically identifies a business for GST, invoicing, and business tax purposes. A business typically holds both.