After I add investment income of total $902, including $140 div, $509 int and $253 capital gain (all short term); tax due increased by $384. How can the tax be so high?

$384 out of $902 means a tax rate > 42% to me, how can it be higher than the highest income tax bucket of 37%? Does anyone know where can I find out how does Turbo tax calculate these numbers? Thank you a lot for your help!