37 Percent Of Low And Moderate Income Taxpayers Have Marginal Tax Rates Of 30 To 39 Percent: CBO Chart

From CBO, "Snapshot of Marginal Tax Rates for Low- and Moderate-Income Workers:"

Marginal tax rates are the percentage of an additional dollar of income that is paid in taxes or given up in government benefits; those rates affect taxpayers’ choices about many things, including how much to work and save. In 2013, 37 percent of low- and moderate-income taxpayers who have earnings face total marginal tax rates—including federal and state individual income taxes, federal payroll taxes, and the phasing out of benefits from the Supplemental Nutrition Assistance Program—between 30 percent and 39 percent, and over 20 percent of that group face marginal rates of 40 percent or more. CBO estimates that 56 percent of such taxpayers face marginal rates of 10 percent to 19 percent from the federal individual income tax system alone.

Source: CBO