The tax table is only one of seven different methods that can be used to calculate your federal tax, depending on what is in your tax return. Your tax return must require one of the other methods. The most common reason that you cannot use the tax table is that your income includes qualified dividends or long-term capital gains, which are taxed at lower rates.
In the 2025 IRS Instructions for Form 1040, look at the instructions for line 16. Starting on page 36 it explains the conditions for determining which of the 7 methods to use to calculate the tax.
If you are using the CD/Download TurboTax software you can see which method TurboTax used by looking at the 7 checkboxes in the Tax Smart Worksheet. You can see the Tax Smart Worksheet in forms mode. It's between lines 15 and 16 in the first section of the Form 1040 or Form 1040-SR Worksheet.
