@soyuppy
The tax rate on long-term capital gain depends on your taxable income, not AGI. For 2020 or 2021, taxable income in on Form 1040 line 15.
There is no 12% tax rate for long-term capital gain. For 2020 and 2021, the tax brackets for long-term capital gain are 0%, 15%, and 20%, depending on filing status and taxable income.
Long-term capital gain is included in the AGI and taxable income on Form 1040, but the tax is calculated separately. The tax calculation is done on a worksheet, usually the Qualified Dividends and Capital Gain Tax Worksheet, or possibly the Schedule D Tax Worksheet.
