This interactive, free tax calculator provides accurate insight into how much you may get back this year or what you may owe before you file. Free federal and state. The information you enter is automatically saved so if mch have any changes, you can easily make them in seconds to see how they affect your federal tax refund. Tax refunds are calculated by subtracting the amount of federal income taxes withheld from tases total income taxes due for the year. If the amount withheld from your paychecks for taxes exceeds the amount you owe, then you will receive a refund. There are several factors that can impact how much income tax you pay and how much you get back as a refund.