Tax File Number (TFN)
A unique 9-digit number issued by the ATO to identify individuals and organisations for tax purposes.
A Tax File Number (TFN) is a unique 9-digit identifier issued by the ATO to individuals, companies, partnerships, trusts, and other entities. It is used to track your tax obligations and entitlements throughout your life. You are not legally required to have a TFN, but without one your employer must withhold tax at the highest marginal rate (45% plus Medicare levy) from your wages.
You should quote your TFN to your employer (via a TFN declaration form), your bank or financial institution (to avoid withholding tax on interest), your super fund, and Centrelink. Never share your TFN publicly or with unauthorised parties — it is a sensitive identifier similar to a Social Security Number in other countries.
Australian residents can apply for a TFN online through myGov or at a participating Australia Post office. Foreign passport holders in Australia on a valid visa can also apply. Your TFN remains the same for life, even if you change your name or address.
How it works
A Tax File Number is a unique nine-digit number the ATO issues once to an individual or entity, and it stays the same for life regardless of name changes, address changes, or moving in and out of the workforce. It exists so the ATO can track your income, deductions, and tax payments across every employer, bank, and super fund you ever use, rather than starting from scratch each time you interact with the system. Applying for a TFN is free and done online through myGov or in person at a participating Australia Post outlet.
You meet your TFN most directly on the TFN declaration form you fill out when starting a new job, where you also indicate whether you want the tax-free threshold applied to that employer's withholding. You quote the same number to your bank so interest isn't taxed at the top rate, to your super fund so contributions are taxed correctly, and to Centrelink if you receive government payments. It follows you through every tax return you ever lodge, linking each year's assessment to the same taxpayer record.
Having a TFN is not legally compulsory, but the consequence of not quoting one is steep: your employer must withhold tax from your wages at the highest marginal rate plus the Medicare levy, rather than using the standard tables that account for the tax-free threshold. People sometimes assume a TFN is only needed once they start working, but it's worth applying as soon as you're eligible, since a missing TFN means waiting until tax time to recover any over-withheld tax. Never share your TFN casually — treat it like a password, not an ID to hand over on request.
Example: withholding without a TFN
Suppose you start a casual job paying $600 a week but haven't yet applied for a TFN, or you decline to provide one on the declaration form. Instead of the standard withholding tables, which build in the tax-free threshold and apply the ordinary marginal rates, your employer must withhold tax at the top marginal rate of 45%, plus the Medicare levy, from the whole $600.
On that $600, 45% alone comes to $270 withheld before the Medicare levy is even added — a far bigger bite than the standard tables would take from the same pay, since those tables assume none of your income is taxed until you're well past $18,200 for the year. The gap between the two outcomes is the practical cost of not having a TFN on file.
Related Terms
ATO (Australian Taxation Office)
The government agency responsible for administering Australia's tax and superannuation systems.
Australian Business Number (ABN)
A unique 11-digit number identifying a business entity to government and the community.
Tax Return
An annual form lodged with the ATO reporting your income, deductions, and tax payable or refundable for the financial year.
PAYG Withholding
The system where employers withhold income tax from employees' wages and remit it to the ATO throughout the year.