I bought last years software and would like to do my sons taxes from last year. Do I have to purchase the software again?

[VolvoGirl]

What did you buy?  Did you pay for the 2015 online version or did you buy the Desktop CD/Download program?  "software" usually refers to the Desktop installed program.  So if you do have the 2015 Desktop program you can use it to prepare multiple 2015 returns.

Or by last year do you mean 2016?

[jerry2000 · Accepted solution]

Turbotax Online works only for current year (2016) taxes, and not for any other year.
If you want to use TurboTax for any other year you will need to purchase the Desktop Version for each year that you need to file. You can do that at this link:
http://shop.turbotax.intuit.com/personal-taxes/past-years-products.jsp

You can download the Forms and Instructions free from the IRS web site at this link:
http://www.irs.gov/app/picklist/list/priorFormPublication.html

In any event, you have to file the return by mail. Turbotax does not support e-file of prior year returns. Tip: If you prepare multiple years of prior returns, mail each one to the IRS in a separate envelope to be sure that each one is recognized as a separate tax return.