How is the tax figured in 12a on a 1040-SR federal form?

[SusanY1]

The tax on Line 12a is a compilation of taxes including all of the following:

• Tax on your income - computed typically from a variety of worksheets depending on the nature of the income or from the tax tables.  There are separate worksheets for various types of income, including qualified dividends and capital gains, which are not taxed based on the tax tables.
• Tax from Form 8814 (election to report a child's interest and dividends on the parent's return).
• Tax from Form 4972 (relating to lump-sum distributions). 
• Recapture of education credit.
• Any tax from Form 8621, line 16e relating to a section 1291 fund.
• Repayment of excess health coverage tax credit from Form 8885.
• Tax from Form 8978 (relating to section 6226 liability).
• Net tax liability deferred under section 965(i) (related to retained earnings in a controlled foreign corporation).

For MOST taxpayers, the number is primarily made up of tax on income from the tax tables plus any income on dividends and capital gains.