With President Obama expected to use his second-chance debate this week to portray Mitt Romney as an uncaring rich guy, a new analysis of the GOP candidate's wealth shows that the millionaire was so generous that he kept just 42 percent of his income.

Obama's team has mocked the 14.1 percent tax rate that Romney is in as shirking his responsibility. But Charlottesville, Va.-based Marotta Wealth Management, which pens a widely-followed research blog, found that when Romney's tax burden and charitable gifts are included, he paid out 57.9 percent of his income.

"Giving $2.3 million to charity certainly should not be the basis of any criticism," said David Marotta. "It is money the Romney's did not keep for themselves, so I am counting it with the money lost to taxes."

His basic math for Romney's 2011 return: $18.6 million in income minus $10.8 million in taxes and charity results in a net of $7.8 million, 42.1 percent of gross. Ditto for 2010, said Marotta.