A Congressional Budget Office study released this week cites higher tax revenues and better-than-expected payments from government-controlled mortgage giants Fannie Mae and Freddie Mac as the key reasons for this year's improved outlook. The budget office now predicts a 2013 budget deficit of $642 billion, more than $200 billion below its February estimate. This year's shortfall would register at 4 percent of the economy, far less than the 10.1 percent experienced in 2009 when the government ran a record $1.4 trillion deficit.

Last year's deficit was $1.1 trillion, capping four consecutive trillion dollar-plus deficits during President Barack Obama's first term. Obama inherited an economy in recession, which stunted tax revenues for several years.

The deficit picture is expected to continue to improve next year and beyond, with the 2015 deficit now projected at $378 billion, just 2.1 percent of the economy. All told, the budget office predicts deficits over the coming decade of $6.3 trillion, down $618 billion from earlier projections.