According to the United States Internal Revenue Service, companies and citizens in the country failed to pay up to $385 Billion in taxes in 2006. The amount that was not paid in 2006 was higher then the estimated $290 Billion that was lost in 2001.
In 2006, the US government had a budget deficit of $248.2 Billion dollars, meaning that if the IRS was able to collect the amount that was not paid, the federal government would have had a surplus of $136.8 Billion.
$235 Billion of the taxes that were not paid in 2006 were from individual taxes.
Source: Steven Sloan, “IRS: Americans Underpaid Taxes by $385B in 2006,” Bloomberg, January 6, 2012.