You may have heard the claim that about half of Americans pay no federal income tax. That’s a true fact. My Tax Policy Center colleagues estimate, for example, that 46% of households either will pay no federal income tax in 2011 or will receive more from the IRS than they pay in.

Today, TPC released a new study that examines why these people end up paying no federal income tax.

The number one reason should come as no surprise. It’s because they have low incomes. As my colleague Bob Williams notes:

A couple with two children earning less than $26,400 will pay no federal income tax this year because their $11,600 standard deduction and four exemptions of $3,700 each reduce their taxable income to zero. The basic structure of the income tax simply exempts subsistence levels of income from tax.

Low incomes (or, if you prefer, the standard deduction and personal exemptions) account for fully half of the people who pay no federal income tax.

The second reason is that for many senior citizens, Social Security benefits are exempt from federal income taxes. That accounts for about 22% of the people who pay no federal income tax.

The third reason is that America uses the tax code to provide benefits to low-income families, particularly those with children. Taken together, the earned income tax credit, the child credit, and the childcare credit account for about 15% of the people who pay no federal income tax.

Taken together, those three factors — incomes that fall below the standard deduction and personal exemptions; the exemption for most Social Security benefits; and tax benefits aimed at low-income families and children — account for almost 90% of the Americans who pay no federal income tax.

For further details and info about the other 10%, please see the study.

P.S.: The true fact — about half of Americans do not pay federal income taxes — often gets transmogrified in public discourse into the decidedly untrue claim that half of Americans pay no taxes. That simply isn’t so. There are many other taxes in our fair land, including payroll taxes, excise taxes, sales taxes, state income taxes, and property taxes. Most people who don’t pay federal income taxes still encounter some of these other taxes.