TurboTax

TurboTax is a series of tax preparation programs for the U.S. federal and state income tax.

The government ensures continued employment for the producers of tax programs by changing the laws, regulations, and forms every year, necessitating corresponding changes to all the software. As a result, programs such as TurboTax use a different file format every year to correspond to the tax forms the data is intended to fill out.

For a while, TurboTax used the .tax extension for its data, but eventually switched to a year-specific extension like .tax2012. Each year's program will only directly open that year's data, though they can import data from past years' returns where this is useful for carrying things over. (To this end, the program will generally recognize the last few years' formats for TurboTax, and even competing programs such as that of H&R Block.)

The format appears to be a proprietary binary format, with the first four bytes spelling "TTFN" in ASCII (54 54 46 4E in hexadecimal), apparently the "signature bytes" indicating that a file is of a TurboTax format. (Ta Ta For Now? No, it probably stands for something like Turbo Tax Financial Network.)

There does not appear to be any documentation of the specifics of the file format online, though the fact that competing tax programs are able to import past returns in the format implies that their makers somehow managed to either obtain or reverse-engineer the format.

Links

 * Official site
 * Official documentation on finding and opening earlier years' tax files (opening them requires obtaining the earlier TurboTax software)