TAX is a file format used by a software tool for TAX returns called TurboTax. The TAX file is used by the Turbo Tax package to store TAX declarations of both individuals and companies. These files are stored and TAX returns for earlier periods can be accessed if needed.

TurboTax is a software released by Intuit Inc. used in the United States and Canada. In Canada, TAX files are used in the certified NETFILE format.