A Sotheby's auction house employee holds a 24.78 carat pink...

A Sotheby's auction house employee holds a 24.78 carat pink diamond mounted as a ring that sold this past November for $46,158,674, smashing the world record for a jewel sold at auction. (November 2010) Credit: AP

As millions of procrastinators scramble to meet Monday's tax filing deadline, ponder this: The super rich pay a lot less in taxes than they did a couple of decades ago, and nearly half of U.S. households pay no income taxes at all.

The Internal Revenue Service tracks the tax returns with the 400 highest adjusted gross incomes each year. The average income on those returns in 2007, the latest year for IRS data, was nearly $345 million. Their average federal income tax rate was 17 percent, down from 26 percent in 1992.

During  the same period, the average federal income tax rate for all taxpayers declined to 9.3 percent from 9.9 percent.

The top income tax rate is 35 percent, so how can people who make so much pay so little in taxes?

The nation's tax laws are packed with breaks for people at every income level. There are breaks for having children, paying a mortgage, going to college, and even for paying other taxes. Plus, the top rate on capital gains is only 15 percent.

There are so many breaks that 45 percent of U.S. households will pay no federal income tax for 2010, according to estimates by the Tax Policy Center, a Washington think tank.

"It's the fact that we are using the tax code both to collect revenue, which is its primary purpose, and to deliver these spending benefits [so] that we run into the situation where so many people are paying no taxes," said Roberton Williams, a senior fellow at the center, which generated the estimate of people who pay no income taxes.

The sheer volume of credits, deductions and exemptions has both Democrats and Republicans calling for tax laws to be overhauled. House Republicans want to eliminate breaks to pay for lower overall rates, reducing the top tax rate from 35 percent to 25 percent.

Republicans oppose raising taxes, but they argue that a more efficient tax code would increase economic activity, generating additional tax revenue.

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