Just who makes up the 47 percent of households that pay no federal income tax? Mitt Romney maligned them as refusing to "take personal responsibility and care for their lives." The Tax Policy Center has the breakdown and Brad Plumer provides analysis in the Washington Post. The reality does not correspond to Romney's fantasy of spoiled freeloaders:
Most of the households in this group don’t pay any federal income tax because they qualify for enough deductions that their income tax liability has shrunk to zero. See this Tax Policy Center report for more, which gives an example of “a couple with two children earning less than $26,400. They get an $11,600 standard deduction and four exemptions of $3,700, and that takes their liability to zero.” Indeed, it’s worth noting that many of these deductions and credits were part of the 2001 and 2003 Bush tax cuts, which Romney wants to extend.
— 10.3 percent of households pay no federal income tax because they’re retired and elderly. Many retirees aren’t taxed on their Social Security benefits, which they earned by paying into the system over many years. If Mitt Romney secretly thinks that these households are all irresponsible freeloaders, he has a weird way of showing it, as he keeps insisting that he doesn’t want to cut Medicare or Social Security benefits for those over the age of 65.
— That leaves 6.9 percent of households which are non-elderly and have incomes less than $20,000 per year and aren’t paying the payroll tax. These poorer households pay neither income taxes nor payroll taxes. Perhaps Romney thinks that they should all pay more in federal taxes. It’s hard to say. But this is also a much smaller fraction of Americans.