Half don't earn enough to pay federal income taxes; many pay other ways.
Well, about half of them don't owe income tax for the simple reason that they don't make enough money. A couple with two children with an income of $26,400 had no income tax liability in 2011, because of an $11,600 standard deduction and four exemptions of $3,700 each, according to the Tax Policy Center (TPC).
"The basic structure of the income tax simply exempts subsistence levels of income from tax," wrote TPC's Roberton Williams in an analysis of these figures last year.
The other half of the untaxed (that's equal to about 23 percent of total US households) claims their status because of particular tax breaks. Many of them are seniors who benefit from the exclusion of some Social Security income. The elderly make up about one-fifth of all non-income-tax-payers. The other big chunk is parents who benefit from tax credits for children and the Earned Income Tax Credit (EITC).