Tax file number

A tax file number (TFN) is a unique identifier issued by the Australian Taxation Office (ATO) to each taxpaying entity—an individual, company, superannuation fund, partnership, or trust. Not all individuals have a TFN, and a business has both a TFN and an Australian Business Number (ABN). If a business earns income as part of carrying on its business, it may quote its ABN instead of its TFN.

The TFN was introduced initially to facilitate file tracking at the ATO, but has since been expanded to encompass income and other data matching. The TFN consists of a nine digit number, usually presented in the format nnn nnn nnn. Strict laws require that TFNs may be recorded or used only for specifically authorised tax-related purposes.

The TFN serves a purpose similar to the American Social Security number, but its use is strictly limited by law to avoid the functionality creep which has affected the US counterpart. It also serves a similar function as national insurance in the UK.