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Australia TFN Validator

Finance & Global IDs

Validate an Australian Tax File Number (TFN) using the official ATO checksum algorithm. Check the format instantly, entirely in your browser.

What is a Australia TFN?

An Australia TFN Validator checks whether a Tax File Number follows the correct structural format the Australian Taxation Office (ATO) uses when issuing these numbers — a 9-digit number with a specific weighted checksum that catches the overwhelming majority of typos and invalid numbers immediately. A TFN is required for nearly every formal financial and employment interaction in Australia, making it worth verifying before submitting it on an important form.

This validator applies the ATO's published checksum algorithm directly, telling you immediately whether a number is correctly formed. For the equivalent Australian business identifier, see the Australia ABN Validator, and for other countries' national tax identifiers, see the UK NIN Validator and Canada SIN Validator.

How to use this Australia TFN calculator

  1. Enter the Tax File Number in the Tax File Number field, with or without spaces.
  2. Read the result card to see whether the number passed validation.
  3. If it failed, check the details breakdown to see the calculated checksum value.
  4. Compare the number against your TFN confirmation letter or official ATO document to find the discrepancy.
  5. Correct the number and re-check until it passes.

Formula & Methodology

A 9-digit TFN is validated using a weighted modulo-11 checksum:

1. Multiply each digit 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.

Frequently Asked Questions

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 purposes. It's required for employment, opening bank accounts, claiming government benefits, and filing tax returns in Australia.
The validator confirms the number is exactly 9 digits, then applies the ATO's published checksum algorithm — multiplying each digit by a specific weight, summing the results, and checking that the total is evenly divisible by 11. This catches the vast majority of mistyped or invalid TFNs.
Each of the 9 digits is multiplied by a corresponding weight (1, 4, 3, 7, 5, 8, 6, 9, 10 respectively), the nine products are summed, and the TFN is valid if that sum is exactly divisible by 11. This is the same modulo-11 checksum approach used by several other national ID systems.
No — a passing checksum only confirms the number is structurally well-formed according to the ATO's numbering algorithm, not that it has actually been issued or belongs to a real person. Confirming an actual TFN requires official verification through the ATO.
No — this validator checks the standard 9-digit TFN format issued to individuals. Older 8-digit TFNs, historically issued to some non-individual entities, use a different checksum and aren't supported by this tool.
Yes — TFNs are commonly displayed in a 3-3-3 grouped format (like 123 456 782), and this validator accepts that format as well as a continuous 9-digit string, stripping spaces automatically before checking.
No — validation happens entirely in your browser using JavaScript. Your TFN is never sent to a server, logged, or stored, which matters given how sensitive this number is.
The most common reasons are a mistyped digit, a missing or extra digit, or a number that was never a real TFN to begin with — such as a randomly made-up number used as a placeholder. Double-check the number against your TFN confirmation letter or official ATO correspondence.
A TFN identifies an individual or entity for personal or entity-level tax purposes, while an ABN (Australian Business Number) specifically identifies a business for GST, invoicing, and business tax purposes. Use the [Australia ABN Validator](/australia-abn-validator/) for checking business numbers instead.
Your TFN appears on your TFN confirmation letter from the ATO, your income tax return notices, and payment summaries from employers or super funds. If you've lost your TFN record, you can request confirmation directly through the ATO's online services.
Also known as
TFN checkertax file number validatorAustralia TFN checksumverify TFNATO tax file number check