There are 7 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. VolvoGirl explained one of the 7 methods above.
The conditions for determining which of the 7 methods to use are explained on page 36 of the DRAFT 2025 IRS Instructions for Form 1040. (The IRS has not yet published the final instructions for 2025.)
If you are using the desktop TurboTax software you can see which method TurboTax used by looking at the 7 checkboxes in the Tax Smart Worksheet in forms mode. The Tax Smart Worksheet is between lines 15 and 16 in the first section of the "Form 1040 or Form 1040-SR Worksheet."
