It doesn't work that way unless your only income is LTCG and Qual Div. First other income is taken into account. then LTCG and Qualified dividends are added to determine what tax bracket they fall into
for example a single person using the standard deduction with about $53,000 in other income and $47,000 of LTCG/Qual dividends would pay 15% tax on about $38,000 of that $47,000
