The fact that the long-term capital gains are included in the "taxable income" on Form 1040 does not mean that you are actually paying tax on the gains. (Technically the gains are taxable, but they are taxed at a 0% tax rate.) The tax calculation takes the 0% rate into account. To see how the tax is calculated you have to look at the worksheet where the calculation is done. Depending on what is in your tax return, the tax is probably calculated on the Qualified Dividends and Capital Gain Tax Worksheet, or possibly the Schedule D Tax Worksheet.
Note that the 0% rate applies only to long-term capital gain.
