WASHINGTON (AP) — Mitt Romney and his wife, Ann, paid $1.94 million in federal taxes on last year's income of $13.7 million, for an effective tax rate of 14.1 percent, his campaign said Friday.

That's slightly above the 13.9 percent rate the couple paid in 2010. Most of the 2011 income was from investments.

Campaign officials said the couple filed the return Friday with the Internal Revenue Service, after receiving an extension. They were to publicly release their full 2011 returns late Friday.

Romney's taxes have emerged as a key issue during the 2012 presidential race with President Barack Obama. Romney released his 2010 tax returns and a 2011 estimate in January, but he has declined to disclose his returns from earlier years.

His vast fortune and his long association with Bain Capital, the private equity firm he cofounded, have been much discussed this year.

His campaign earlier estimated that Romney would pay about $3.2 million in taxes for the year, an estimate well above the $1.9 million actually paid. He paid about $3 million in federal income taxes in 2010 — an effective rate of 13.9 percent.

Critics, including Obama, have urged Romney to release more than just the two years of returns and follow his father's model. When George Romney ran for president, he released 12 years of tax returns.

Mitt Romney's campaign did put out a summary Friday by Brad Malt, the trustee of the couple's blind trust, saying that over the 20-year 1990-2009 period, the Romneys owed both state and federal income taxes and paid federal taxes at an effective annual rate of 20.2 percent

Obama's own tax return for last year showed that he and his wife, Michelle, paid $162,074 in federal taxes on $789,674 in adjusted gross income, an effective tax rate of 20.5 percent. Their income plunged from $1.7 million in 2010, with declining sales of the president's books. In 2009, the Obamas reported income of $5.5 million, fueled by the best-selling books.

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The Romneys' exact totals for 2011 were federal taxes of $1,935,708 and on income of $13,696.951.

Most of Romney's income is from investments held in a blind trust, and campaign aides have stressed that he makes no decisions on how his money is invested.

During the 20-year period, the Romneys paid an effective federal income tax rate of between 13.45 percent and 13.66 percent each year, trustee Malt wrote.

For last year, the Romneys claimed a deduction for $2.25 million of their $4.021 million in charitable contributions, Malt said. In the previous year, a large percentage of those contributions went to the Mormon Church.

They could have claimed a higher charitable deduction, Malt said, but the couple "limited their deductions of charitable contributions to conform to the governor's statement (n August, based on the January estimate of income, that he paid at least 13 percent in income taxes in each of the last 10 years."

Romney told reporters in August that he's never paid less than 13 percent of his income in taxes during the past decade. He said that Democratic Senate Majority Leader Harry Reid's claim to have heard that he paid no taxes in some years was "totally false."

The former Massachusetts governor, who would be among the richest presidents ever elected, is aggressively competing with Obama for the support of middle class voters. Romney has estimated wealth of as much as $250 million.

His tax rate of 14.1 percent is below that of many Americans because most of it flows from capital gains, which are taxed at 15 percent whereas the top marginal income tax rate now is 35 percent.

On average, middle-income families, those making from $50,000 to $75,000 a year, pay 12.8 percent of their income in federal taxes, according to Congress' Joint Committee on Taxation.

Several tax law experts said Friday that Romney's newly released tax returns would not be much help in uncovering the most persistent mysteries of the candidate's sprawling finances — whether he used aggressive tax-deferral strategies, what are the specifics and tax advantages of his numerous offshore investments, what is the source of his massive retirement account and what are the details behind his now-closed $3 million Swiss bank account.

The analysts said those details could emerge only if Romney provided far more of his tax returns — including files dating back to his years at Bain Capital, the private firm he left in 2001. Romney, who initially refused to disclose any tax returns, has drawn the line at providing only his 2010 and 2011 returns.

"The issue has never been Romney's 2011 tax return — in fact, it is a distraction to the real issues," said Edward D. Kleinbard, a law professor at the University of Southern California and former chief of staff of Congress' Joint Committee on Taxation. "All the important compliance and policy questions relating to Romney's personal tax matters relate to the past."

Only multiple returns would provide details about Romney's $100 million retirement account and how it grew, Kleinbard said. He also earlier returns would be crucial in knowing how often he paid gift tax on family trusts.

Joseph Bankman, a Stanford University law school professor and expert on tax law, said Friday, "It's the Bain years we'd really need to know to have a full assessment of his tax strategies." Bankman said that the 2010 and 2011 returns "only raised these questions, but they can't provide real answers."