TFN Checker (Australia)

TFN Checker tells you whether an Australian Tax File Number is correctly formed. Every TFN carries a built-in check: multiply each digit by a fixed weight, add the results, and a real TFN always gives a total that divides exactly by 11. A typo, such as one wrong digit, almost always breaks that rule, so the check catches most mistakes before a form goes in.

It is made for payroll officers checking a new starter’s declaration, bookkeepers cleaning up a staff list, students learning how check digits work, and software testers who need to know why a number fails. Type one number to see the verdict with the full working, or paste a whole list to get a valid and invalid table you can copy or save as a spreadsheet file.

A TFN is private, so this tool is built to keep it that way. It is a format check only: it does not look anything up and can’t tell you whose number it is. The maths runs in your browser, nothing is saved or sent, and both boxes empty themselves when you leave the page. To confirm a TFN belongs to someone, they can see it in their myGov account or contact the ATO.

1. Type or paste the number into “Tax File Number”. Spaces and dashes are fine; it groups the digits for you.
2. Read the verdict as you type: green for correctly formed, red with the reason when it isn’t.
3. Look at “How the check works” to see each digit, its weight, the products, the total and the remainder.
4. Press “Hide digits” if someone can see your screen, and “Clear” when you are done.
5. For many numbers, open “Check a list”, paste one per line, then use “Copy results” or “Download CSV”.

• Checks 9-digit TFNs with the weights 1, 4, 3, 7, 5, 8, 6, 9 and 10, and older 8-digit TFNs with 10, 7, 8, 4, 6, 3, 5 and 1.
• Live result as you type, with automatic grouping into 123 456 782 style.
• The full working: a digit × weight table, the total and the division by 11, so you can follow or teach the method.
• Plain reasons for every fail: wrong length (and a hint when 11 digits looks like an ABN), stray letters, or a total that doesn’t divide by 11.
• Typo help: when swapping two neighbouring digits would pass, it says which ones.
• Batch mode for up to 5,000 numbers, separated by new lines, commas, semicolons or tabs, with a summary count.
• Copy the results table or download a CSV that opens straight in Excel, Numbers or Google Sheets.
• Hide digits on screen, and both boxes clear themselves when you close or leave the page.

• A pass means the number is possible, not that it is real or belongs to the person who gave it. Treat it as a typo check.
• All zeros passes the sum but is never issued, so the checker marks it as not a real TFN.
• The rule for older 8-digit TFNs is less widely documented than the 9-digit one, so treat an 8-digit fail as a strong hint and check the source.
• Don’t email TFNs or keep them in shared spreadsheets. If you download a CSV, store it securely and delete it when you are finished.
• Checking a business number instead? Use the ABN Validator, which also handles ACNs.