The campaign released a summary of Romney's 2011 returns, which were filed Friday. The returns filed by Romney and three affiliated trusts will be posted online at 3 p.m., the campaign said.
Romney and his wife, Ann, have paid 100 percent of the taxes they owe, Brad Malt, a partner at the law firm of Ropes & Gray LLP in Boston who manages the Romneys' investments, wrote in a blog post on the campaign's website.
Romney makes most of his income from investing an estimated $250 million fortune, and much of that income is taxed at a top rate of 15 percent, rather than the top rate of 35 percent that applies to wages. Romney, 65, is a former Massachusetts governor and co-founder of Bain Capital LLC, the Boston-based private equity firm.
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Romney had previously released his 2010 tax return, which showed that he paid a 13.9 percent rate on $21.7 million in income. Democrats have criticized Romney for not releasing more years of tax returns. Senate Majority Leader Harry Reid, a Nevada Democrat, has said he was told by someone with knowledge of Romney's finances that he hadn't paid any federal income taxes in some years.
Romney has said he paid a minimum tax rate of 13 percent in each of the past 10 years. To stay above that level for 2011, Malt wrote, Romney claimed deductions for $2.25 million of his $4 million in charitable contributions.
The Romneys made the charitable contributions during 2011. Earlier this year, when the campaign released their estimated 2011 tax return, the couple's projected income was $20.9 million, so the contributions as a share of income would have been lower than they ultimately were.
The campaign's statement Friday doesn't explain the difference between that projection and the Romneys' actual income of $13.7 million.
The campaign said it will release a letter from PricewaterhouseCoopers LLP, which prepares Romney's returns, summarizing his filings for the past 20 years. During that period, from 1990 through 2009, Malt wrote, Romney's average annual effective federal tax rate was 20.2 percent and the lowest rate he paid in that period was 13.7 percent.
With the first debate less than two weeks away, Romney aides wanted to put some distance between the release of the tax returns and the head-to-head matchup with President Barack Obama.
Still, the news that Romney had a 14.1 percent effective tax rate probably will reignite Democratic criticism that Romney is too wealthy to connect with average voters and is hiding something by refusing to release more than two years of returns.
"Tax havens, offshore accounts, carried interest," said the narrator of an Obama campaign ad that ran in July. "Mitt Romney has used every trick in the book." The commercial ends with: "Makes you wonder if some years he paid any taxes at all." Obama and his wife, Michelle, filed their 2011 tax returns in April. They reported paying a 20.5 percent federal tax rate on $789,674 of adjusted gross income.
Romney has previously said that paying more taxes than required should disqualify him from becoming president.
"I don't pay more than are legally due, and frankly if I had paid more than are legally due I don't think I'd be qualified to become president," he said in an interview with ABC News on July 29. "I'd think people would want me to follow the law and pay only what the tax code requires."
Romney gave in to public pressure during the Republican primaries to release his 2010 tax return, saying at the time that he would disclose his 2011 filing later in the year, when it was completed. He had requested an extension and the return filed Friday was due by Oct. 15.
His father, George, a onetime Michigan governor, released 12 years of tax returns when he ran for president in 1968. Mitt Romney gave 23 years of filings to Republican presidential nominee Senator John McCain of Arizona when Romney was being considered for the vice presidency in 2008.
Romney has said repeatedly that he has no intention of releasing additional returns. Aides say they don't want to do anything that would distract from their strategy of making the election about Obama's stewardship of the economy. They also worry that this could be a political trap set by their rivals, advisers said.