Income is taxed in the United States at the federal level using marginal tax rates for most earnings, according to the Tax Foundation. Marginal tax rates exist when individuals pay varying tax rates on different earnings increments, according to Investopedia.
In the United States, individual income is taxed at seven different rates as of 2015, ranging from 10 to 39.6 percent, according to the Tax Foundation. Each rate corresponds to income in a certain range, depending on one's status as single, married filing jointly, married filing separately or head of household. For example, a single filer with income up to $9,225 is taxed at 10 percent, while income from $9,225 to $37,450 is taxed at 15 percent. Income above a certain threshold, ranging from $413,200 to $464,850 depending on taxpayer status, is taxed at a flat rate of 39.6 percent.