Federal income tax rates for 2015 range from 10 to 39.6 percent depending on the taxpayer's filing status and income, according to Bankrate. The lowest rate applies to single workers and married couples with less than $20,000 in earnings, while incomes over $400,000 are taxed at 39.6 percent.
Each tax rate applies to a range of incomes known as a tax bracket. For single and head-of-household taxpayers, tax bracket determines tax rate, as noted by Bankrate.
Whether married taxpayers file jointly or singly influences how much tax they pay. A married couple with individual incomes of $30,000 and $80,000 that files jointly falls into the 25 percent tax bracket. Filing separate returns, however, drops the $30,000 income to the 15 percent bracket and bumps the $80,000 income into the 28 percent bracket, Bankrate states.