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).
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.
History
TFNs have been used by the ATO since the 1930s.
At some point in time between 1972 and 1983 the format of tax file numbers changed. The earlier format was still in use in 1972, and the later format was in use by 1983.
thumb|Notice of amended assessment 1969 – with tax file number T92737
Under the later format, the TFN itself was either 8 or 9 digits, with a check digit. Individuals received a 9 digit TFN and non-individuals received an 8 digit TFN. The quote of the TFN was not obligatory when, for example, lodging a tax return, though failing to quote one may delay the processing of the tax return.
thumb|Notice of assessment 1972 - still using the tax file number/format T92737
thumb|Notice of amended assessment 1982 – with a 9 digit tax file number 330 600 376
In May 1988, following the demise of the Australia Card scheme, the Treasurer Paul Keating announced that the Government intended to introduce an enhanced TFN scheme, and legislation establishing the scheme was passed that year.
When the legislation was introduced in 1988 the 8 and 9 digit TFN scheme still applied. However, as the 8 digit TFNs were becoming exhausted, all new taxpayers are issued 9 digit TFNs.