There can be many facets to calculating your federal income tax. It can be affected by different types of income such as self-employment income, premium tax credit repayments, alternative minimum taxes, net investment taxes well as tax penalties. It can be much more involved than simply looking up your tax in a table based on your taxable income.
I suggest you look your form 1040 and schedules 1 to 3 to learn more about the different types of income listed on your tax return, as well as the different types of taxes that may be listed. You can also look at your Tax Smart Worksheet after you pay for your program to learn more about how your tax is calculated:
To view your form 1040 and schedule 1 to 3: