There are seven different methods that can be used to calculate the tax on Form 1040 line 16, depending on what types of income you have and other things in your tax return. In TurboTax there is a Tax Smart Worksheet that has 7 checkboxes that show you which method TurboTax used. If you are using the download TurboTax software, go to forms mode and open the Form 1040 or Form 1040-SR Worksheet. The Tax Smart Worksheet is between lines 15 and 16 in the first section of the Form 1040 or Form 1040-SR Worksheet.