In general, this depends on how a program gets installed on a computer: for a single user, or for all users. If I remember right, TurboTax installs to be available to all users. In this case, you cannot install a second copy on the same computer, but you can use the one already installed to enter and file a second tax return. TurboTax allows you to file up to 5 Federal returns from a single installation. Some versions also include filing in one state. You can buy filing additional state returns in the program.