Capital Gain from Long Term Stock Sale is calculated to be at 18.9 % instead of 15%

Turbo Tax seems to calculate capital gain from my long term stock sales wrong.  I compare the "Federal Tax  Due" from before I enter the capital gain versus that of after capital gain,  it shows that capital gain is taxed at about 18.9% rather than 15%.   Does Turbo Tax have issues in calculating capital gain tax?