How exactly does long term cap gains tax work when diluted with regular income in the same year?

[Boyan]

Hi everyone,

My scenario's objective is simple: pay zero income tax.

The mechanics: we know that taxable income in tax year 2025 below (Single Filers: Taxable income up to $48,350) will pay $0 in long term cap gains tax. However if one has $30k of deductions (mortgage interest plus property taxes) I postulate that such use case will permit to take an additional $30k distribution out of a 401k since it will be negated by the deductions so taxable income is still kept at bay for the $0 tax LT cap gains goal.

However how would that work out in terms of income tax on the $30k? Which bucket of income (1) or (2) will the deductions apply to? The taxable income will still be less than $48,350/year but it's made up by two different income sources. Please enlighten me! 

[Opus 17]

Capital gains stacks on top of your regular taxable income.

Suppose your taxable regular income (after all deductions) is $30,000.  Then, the first $18,350 of capital gains will be taxed at zero percent, because your total taxable income is under $48,350.  Every dollar of capital gains above that will be taxed at 15%, because your total income puts you in the bracket where regular income would be taxed at 22% and LTCG are taxed at 15%. 

[VolvoGirl]

How much are your capital gains?   They are included in the taxable amount  that determines how much capital gains tax you pay.