Tax file numbers (TFN) rules explained: do you need one, and who can you give it to?

By FastBuySale Newsroom · 5 Nov 2026 · 25m ago

What a TFN is and why it matters

Tax file numbers (TFN) rules explained simply: a TFN is your personal reference number in Australia's tax and superannuation systems. It is free to apply for one, you can apply at any age, and it is yours for life, even if you change jobs or name, move interstate or go overseas.

You don't legally have to have a TFN, but the Australian Taxation Office (ATO) says that without one your employer or bank must withhold more tax from payments to you, you can't lodge your tax return online, you can't apply for an Australian business number (ABN), and you can't claim government benefits such as JobSeeker.

The ATO describes your TFN as a unique number, usually nine digits, and an important part of your identity. It is how the ATO and your super fund match your income, tax and contributions to you.

You'll need it at key moments. The ATO lists starting a new job, applying for government benefits, lodging a tax return and applying for higher education loans.

When you start a job, you normally give your TFN through a Tax file number declaration. The ATO says you should complete one before you start receiving payments from a new payer, including payments as an employee, company director or office holder, labour hire payments, benefit and compensation payments, and super benefits. The declaration lets your payer work out how much tax to withhold.

You don't need a new declaration in some cases, for example if you are receiving super benefits and have already quoted your TFN to the fund's trustee.

Readers evaluating Tax file number should separate marketing claims from the actual rule text that governs their account or product. When two summaries disagree, the governing document or statute wins. If a rule depends on your age, filing status, or income band, re-check it when any of those facts change. Life events quietly move people across thresholds they last reviewed years earlier.

How to apply for a TFN

Applying is free. The ATO offers online or paper applications depending on your circumstances and residency status, with separate processes for Australian residents, permanent migrants and temporary visitors with a valid work rights visa, people living outside Australia with Australian-source income, Norfolk Island residents, and Aboriginal and Torres Strait Islander people.

Australian citizens aged at least 15 can apply online using a Digital ID such as myID with a Strong identity strength. The ATO says this online process may mean you receive your TFN much sooner.

Otherwise, you'll generally receive your TFN within 28 days after the ATO receives your completed application and required identity documents. It is sent to the postal address on your application or your myGov Inbox, depending on how you apply. If it hasn't arrived after 28 days, contact the ATO.

Already have one but forgot it? The ATO says you can find it in the ATO app or your ATO online account via a linked myGov account, on your notice of assessment, on some ATO letters, on an income statement or payment summary from your employer, or on your super statement. A registered tax agent can also tell you.

A useful habit is to write down your goal, time horizon, and cash buffer before you change any election related to Tax file number. Decisions made during a stressful week are the ones people reverse later at a cost. Educational explainers like this one cannot replace personalized advice for complex situations such as divorce orders, inherited accounts, or cross-border tax residency. Escalate those cases to a qualified professional.

Who you should, and shouldn't, give your TFN to

The core rule is to share it only when there is a legitimate reason. The ATO lists the legitimate recipients: the ATO itself when discussing your tax records, your employer when you start work, your bank or financial institution, other government agencies when claiming benefits, your super fund and your university.

Everyone else should be treated with suspicion. The ATO warns that someone only needs basic details, such as your name, date of birth, address, myGov details or TFN, to commit identity fraud or scams.

Practical habits help: don't include your TFN on a job application or résumé, don't share it on social media or in a reply to an unsolicited message, and store documents that show it, such as notices of assessment, securely.

If you're unsure whether a request is genuine, contact the organisation using contact details you find yourself rather than ones supplied in the message.

Keep digital and paper copies of confirmations after every change. Screenshots of election pages, email receipts, and year-end statements make tax season and job changes far less chaotic. Compare fees the same way you would compare two similar listings before you buy: look at what you pay each year, what you get, and whether a simpler option meets the same need.

Your TFN and your super

Giving your TFN to your super fund matters more than many people realise. The ATO tells funds that it is the primary locator used to link contributions and rollovers to member accounts and to help consolidate super across funds.

If your fund doesn't have your TFN, it may be liable for additional income tax of 32% on top of the usual 15% contributions tax on assessable contributions, such as employer and salary sacrifice contributions. For accounts opened on or after 1 July 2007, the extra tax applies to all the member's contributions for the year, whatever the amount.

Without your TFN, the ATO says funds must also return member contributions or super co-contributions within 30 days of becoming aware they shouldn't have accepted them, unless they obtain the TFN within that time.

Fixing it late can help: when you quote your TFN, the fund may claim back extra tax paid in the three income years before it received your TFN. Check each of your super accounts holds your TFN. You can model the long-term difference with the calculators at

If a rule depends on your age, filing status, or income band, re-check it when any of those facts change. Life events quietly move people across thresholds they last reviewed years earlier. Automation helps. Calendar reminders for annual reviews, automatic transfers, and beneficiary checkups reduce the chance that a good plan dies from neglect.

Keeping it up to date, and if it's lost or stolen

Your TFN never changes, but the details attached to it can. The ATO lets you update your contact details, name, date of birth record, gender and bank details online, by phone or by post, sometimes with an identity document.

If your TFN has been lost or stolen, or an unauthorised person has access to it, tell the ATO as soon as possible. If you suspect misuse, the ATO's Client Identity Support Centre is on 1800 467 033, 8:00 am to 6:00 pm, Monday to Friday.

The centre helps people whose identities have been stolen or misused, giving information and assistance to re-establish identity, and it may apply security measures to monitor unusual or suspicious activity on your account.

More Australian money explainers are at and step-by-step guides at

Found this Tax file number explainer useful? Share it with a friend, tell us what we missed in the comments, and get the FastBuySale app on Google Play () for more guides. Have something to sell? Post a free listing at in a couple of minutes.

Educational explainers like this one cannot replace personalized advice for complex situations such as divorce orders, inherited accounts, or cross-border tax residency. Escalate those cases to a qualified professional. When in doubt about a number that changes every year, describe your plan qualitatively first, then look up the current official figure for the tax year you care about before you act.

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