The right-wing talking point that half of all Americans pay no income tax keeps circulating endlessly. Chuck Marr and Brian Highsmith of the Center on Budget and Policy Priorities gives it the thorough debunking it so badly deserves. Summary:

  • The 51 percent figure is an anomaly that reflects the unique circumstances of 2009, when the recession greatly swelled the number of Americans with low incomes and when temporary tax cuts created by the 2009 Recovery Act — including the “Making Work Pay” tax credit and an exclusion from tax of the first $2,400 in unemployment benefits — were in effect. Together, these developments removed millions of Americans from the federal income tax rolls. Both of these temporary tax measures have since expired. In a more typical year, 35 percent to 40 percent of households owe no federal income tax. In 2007, the figure was 37.9 percent.
  • The 51 percent figure covers only the federal income tax and ignores the substantial amounts of other federal taxes — especially the payroll tax — that many of these households pay . As a result, it greatly overstates the share of households that do not pay any federal taxes. Data from the Urban Institute-Brookings Tax Policy Center show only about 14 percent of households paid neither federal income tax nor payroll tax in 2009, despite the high unemployment and temporary tax cuts that marked that year.
  • This percentage would be even lower if federal excise taxes on gasoline and other items were taken into account.
  • Most of the people who pay neither federal income tax nor payroll taxes are low-income people who are elderly, unable to work due to a serious disability, or students, most of whom subsequently become taxpayers. (In a year like 2009, this group also includes a significant number of people who have been unemployed the entire year and cannot find work.)
  • Moreover, low-income households as a whole do, in fact, pay federal taxes. Congressional Budget Office data show that the poorest fifth of households as a group paid an average of 4 percent of their incomes in federal taxes in 2007 (the latest year for which these data are available), not an insignificant amount given how modest these households’ incomes are — the poorest fifth of households had average income of $18,400 in 2007. The next-to-the bottom fifth — those with incomes between $20,500 and $34,300 in 2007 — paid an average of 10 percent of their incomes in federal taxes.
  • Even these figures understate low-income households’ total tax burden, because these households also pay substantial state and local taxes. Data from the Institute on Taxation and Economic Policy show that the poorest fifth of households paid a stunning 12.3 percent of their incomes in state and local taxes in 2010.
  • When all federal, state, and local taxes are taken into account,the bottom fifth of households paid 16.3 percent of their incomes in taxes, on average, in 2010. The second-poorest fifth paid 20.7 percent.

It's worth pulling out the part about state and local taxes. Our federal system devolves a significant share of government responsibility to state and local government, which overall charge higher tax rates to the poor than to the rich:

You need a progressive federal tax system merely to compensate for the regressivity of state and local taxes. And, of course, conservative politicians at the state and local level favor the most regressive tax systems, and conservative politicians at the federal level favor devolving more federal functions to the state and local level, where they'll be funded by regressive rather than progressive taxation.