You can go and input all your info for free and see how the software does the tax. I do that all the time. This year I found out that TaxAct and TurboTax didn't calculate the correct taxes owed (social security taxed was incorrect) so I then inputted into HRBlock. They did it correctly. How do I know? I am so paranoid about taxes that I make sure to calculate them myself first! Would have been an accountant if I didn't become a math teacher. One year I had to do 3 federal and 9 state returns, just for us and our two kids who moved a lot!