Assuming your $90,000 other income already includes the taxable portion of social security, and you have no other tax attributes (e.g. child tax credit) dependent on AGI, a $77,000 long term capital gain will result in $9840 additional tax. $11,800 will be taxed at 0% and 65,600 will be taxed at 15%.
Turbotax will prepare the "Qualified dividends and capital gains worksheet" to show the tax calculation. The worksheet is complicated because it's designed for
multiple scenarios. But, for your simple situation the calculation goes like
this:
$90,000 Adjusted Gross
income (AGI)
-24,000 Standard deduction
= 66,000 taxable income
$77,400 Threshold for 22% bracket where LTCG are taxed at
15%
-66,000 taxable income
= 11,400 LTCG taxed at 0%
77,000 Total LTCG
-11,400 taxed at 0%
= 65,600 taxed at 15%
65,600 x 0.15 = $9840
