TFN (Tax File Number)
Your personal reference number in the tax system.
A Tax File Number is your personal reference number with the ATO. You give it to employers, your bank and your super fund so your income and tax are tracked correctly. It’s yours for life, stays the same across jobs, and should be kept private — it’s different from an ABN, which identifies a business.
A TFN identifies you as a taxpayer; an ABN identifies a business. A sole trader holds both and uses them for different things — the ABN goes on invoices, the TFN stays private and is how the income eventually lands on your return. You are never obliged to give a TFN, but withholding it has a cost.
Worked example
Give your TFN to a new employer and tax is withheld at the rates that match your income. Leave the declaration blank and the employer must withhold at the top rate instead — you get the difference back at tax time, but only after waiting the rest of the year for it.
Common mistake
Sending a TFN over email or chat because a form asked for it. It is a lifelong identifier that cannot be rotated like a password, so it belongs in the payroll, bank or super portal that needs it — never in a message thread.
Grounded in ATO guidance. Figures last checked . General information, not tax advice.
Related terms
ABN (Australian Business Number)
The 11-digit number that identifies your business.
Sole trader
The simplest business structure — you and the business are one.
Cost of goods sold (COGS)
What the things you actually sold cost you to make or buy.
Trading stock (and the $5,000 stocktake shortcut)
The goods you hold to sell — and when you can skip the stocktake.
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Questions about this term
TFN (Tax File Number): common questions
- Who should I give my TFN to?
- Employers, your bank and your super fund — the places that report your income and tax to the ATO. It belongs in the payroll, bank or super portal that needs it. It never goes on an invoice or to a client; the ABN is the number for business paperwork.
- What happens if I don’t give my new employer a TFN?
- They must withhold tax at the top rate instead of the rates that match your income. You get the difference back at tax time, but only after waiting the rest of the year for it. You are never obliged to hand over a TFN, but withholding it has that cost.
- Is it safe to send my TFN by email or chat?
- Best not to — a TFN is a lifelong identifier that cannot be rotated like a password. It belongs in the secure portal of the employer, bank or fund that needs it, never in a message thread, even when a form seems to be asking for it in a hurry.
- Does my TFN change when I change jobs?
- No — it is yours for life and stays the same across jobs, banks and super funds. You give it to each new employer so your income and tax are tracked correctly, and the same number follows you rather than being reissued.
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