Gingrich's Plan

Ginsberg said Romney would fare better financially under Gingrich's tax plan than under his own. Gingrich would end all taxation of capital gains; Romney wouldn't let high-income taxpayers receive that break.

The 203-page return of Romney and his wife, Ann, along with returns from trusts and a foundation, provide a glimpse into the candidate's financial life. The net worth of the 64-year-old Romney is between $190 million and $250 million, according to an estimate from his campaign.

In 2010, the Romneys had more than $4.5 million in itemized deductions, including almost $3 million in charitable contributions. The couple donated $1.5 million in 2010 to the Church of Jesus Christ of Latter-Day Saints, which also received donations from the family's foundation. They contributed $2.6 million to the Mormon church in 2011, according to the estimated return.

Anthony Nitti, a tax partner at WithumSmith & Brown in Aspen, Colorado, said Romney's return is a "pretty extreme example" of someone receiving income at preferential tax rates on investments.

'High Net Worth'

"For a high net-worth individual, there's nothing here that surprises me," said Nitti, who reviewed the return for Bloomberg News.

The Romneys paid the alternative minimum tax, which is designed to prevent people from avoiding taxes legally. That parallel tax system doesn't eliminate the preference for investment income.

Some aspects of the Romneys' returns indicate that he actually paid a higher tax rate than is stated, said Alan Dlugash, a partner at Marks, Paneth & Shron LLP in New York who also reviewed the returns for Bloomberg News. The tax code limits deductions for certain investment expenses, he said. Also, though the Romneys paid foreign taxes on overseas investments, those payments show up as a credit on the U.S. tax return, making the effective rate to all governments look smaller than it actually is, he said.

"His tax rate's actually higher than what it is," Dlugash said.

Cayman Islands