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Mitt Romney paid $1.95 million in taxes on his 2011 investment income of $13.7 million, his campaign revealed on Friday, making good on Mr. Romney’s promise earlier this year to eventually release his full returns for that year.

Mr. Romney, who made millions by running Bain Capital, a private equity firm, paid an effective federal tax rate of 14.1 percent in taxes, primarily because most of his income was in the form of capital gains that are taxed at a lower rate than ordinary income. Mr. Romney has said that he has paid at least 13 percent in federal income taxes in each of the last 10 years.

In order for that claim to be true in 2011, Mr. Romney had to voluntarily take a smaller deduction than he was entitled to for his charitable deductions, his advisers said Friday.

Mr. Romney and his wife, Ann, donated about $4 million to charity in 2011, but claimed only $2.25 million as a deduction. The campaign said that Mr. Romney’s tax liability would have been far lower in 2011 had the Romneys claimed the full deduction for their charitable contributions.

“The Romneys thus limited their deduction of charitable contributions to conform to the governor’s statement in August, based upon the January estimate of income, that he paid at least 13 percent in income taxes in each of the last 10 years,” said R. Bradford Malt, Mr. Romney’s trustee.

It is possible, however, that Mr. Romney could still deduct the unclaimed amount of his charitable donations in future tax years, experts said.

The Republican presidential nominee, who released his 2010 tax returns in January, continues to refuse demands from President Obama’s campaign and other Democrats to release multiple years of his returns. Mr. Obama has sought to portray Mr. Romney as an out-of-touch millionaire who used off-shore accounts and accounting gimmicks to reduce his tax liability.

In an indication that the summaries will not satisfy Mr. Romney’s critics, Brad Woodhouse, the communications director for the Democratic National Committee, posted the following message on Twitter: “Summaries? What is Romney hiding? This isn’t just abt rates — how about Swiss Bank Accts, Bermuda Shell Cos and Caymans Investments?”

But Mr. Romney released a letter later Friday from his tax advisers providing a summary of his tax liability for a 20-year period from 1990 to 2009. The summary says that Mr. Romney paid taxes every year during that period, that the lowest annual federal tax rate was 13.66 percent and that the Romneys gave an average of 13.45 percent of their income to charity during the period.

The bottom-line numbers provided by Mr. Romney’s trustee were the first to be reported. But answers to more detailed questions will take longer to discover amid the many pages of documents released by the Republican campaign.

Among the questions raised by Mr. Romney’s critics, including advisers to Mr. Obama’s campaign: How much money, if any, did Mr. Romney pay in foreign taxes in 2011? How much money, if any, remains sheltered in overseas accounts? What are his remaining ties to Bain Capital, the firm he founded?

The letter from Mr. Romney’s tax accountants appears to directly contradict unsubstantiated assertions from Senator Harry Reid of Nevada, the Democratic leader. Mr. Reid had asserted this summer that someone told him Mr. Romney paid no federal income taxes at all for ten years.

Mr. Reid made the allegation in interviews and on the floor of the Senate but repeatedly refused to say who provided him the information. Mr. Romney angrily accused Mr. Reid of lying, saying that the top Democrat in the Senate should “put up or shut up.”

In a statement on Friday, Mr. Reid did not repeat his claim, but continued to attack Mr. Romney for a lack of transparency by releasing only summary of most of his tax returns.

“When will the American people see the returns he filed before he was running for president?,” Mr. Reid said. “Governor Romney is showing us what he does when the public is looking. The true test of his character would be to show what he did when everyone was not looking at his taxes.”

Mr. Reid also accused Mr. Romney of “manipulating” his 2011 tax return by deducing less than he was entitled to from charitable deductions so that his effective tax rate was higher.

“That raises the question: what else in those returns has Romney manipulated?” Mr. Reid said.

The letter released on Friday from Price Waterhouse Coopers, Mr. Romney’s tax preparers, said that Mr. Romney paid taxes every year from 1990 to 2009.

“In each year during the entire 20-year period, the Romneys owed both state and federal income taxes,” the company wrote. “Over the entire 20-year period, the lowest annual effective federal personal tax rate was 13.66%.”

For months during the Republican primaries, Mr. Romney refused to release any information about the taxes he had paid, saying the information was not relevant despite a tradition of disclosure by presidential candidates that dates to his father’s 1968 bid for the presidency. George W. Romney released 12 years of returns.

In April, under pressure from his Republican rivals for the nomination and Democratic critics, Mr. Romney had estimated he would owe $3.2 million in taxes on $20.9 million in income during 2011. At the time, he promised to release the full returns before Election Day.

His decision to release the tax documents on a Friday afternoon could help his campaign minimize news coverage of them. Politicians often try to release potentially damaging information just before a weekend, when voters are often paying less attention to their televisions and newspapers.

In spite of the timing, the release of the tax return is almost certain to rekindle the discussion about Mr. Romney’s personal wealth and Democratic attacks that his aggressive use of legal tax avoidance techniques sets him apart from average Americans.

In an Obama television ad, a narrator mentions tax havens, offshore accounts and carried interest and then says: “Makes you wonder if some years he paid any taxes at all. We don’t know because Romney has released just one full year of his tax returns.”

Democrats have sought to link Mr. Romney’s personal tax returns to the tax policies he would pursue if he were elected president. Mr. Obama argues that Mr. Romney’s tax policies are designed to provide tax cuts to wealthy people, which would lead to tax increases for middle-class citizens.

“Governor Romney’s tax plan would actually raise taxes on middle-class families with children by an average of $2,000,” Mr. Obama said last month at an event in New Hampshire. “Not to reduce the deficit, or grow jobs, or invest in education — but to give another tax cut to people like him.”

At a rally in Cincinnati earlier this week, Mr. Obama mocked the complexity of Mr. Romney’s tax returns.

“I’ve actually done my own taxes,” Mr. Obama said. “I don’t know about some of these other folks, but I’ve done them, you know… So I know we can make it more simple and more fair.”

Mr. Romney’s campaign has argued that his personal wealth is not relevant to the broader debate about who is best able to lead the country out of a sluggish economy.

Last month, Mr. Romney said the continued focus on his personal tax returns by his Democratic opponents and the news media was “small-minded” in light of the economic problems that the country faces. His wife, Ann, has said the campaign was resisting a disclosure that would go back years because opponents would use the information against Mr. Romney.

“The more we get attacked, the more we get questioned, the more we get pushed,” Mrs. Romney said in an interview on NBC’s “Rock Center” last month. “There’s going to be no more tax releases given. Mitt is honest. His integrity is just golden.”

But Mr. Romney had little choice but to release the full details of his 2011 tax returns, having promised to do so earlier in the year.

In an amended return, Paul Ryan, the vice presidential candidate, told the I.R.S. he and his wife had “inadvertently” failed to report $61,122 in income from 2011. That raised their total income to $323,416 and increased their taxes by $19,917 to $64,674, or 20 percent of adjusted gross income.

They owed a penalty of $59 for the original underpayment.

They explained that they had overlooked their income from the Prudence Little Living Trust. Mrs. Little, who died in 2010, was Mrs. Ryan’s mother.

In a statement, Stephanie Cutter, the deputy campaign manager for Mr. Obama, said Mr. Romney’s 2011 tax return confirms that “people like Mitt Romney pay a lower tax rate than many middle class families because of a set of complex loopholes and tax shelters only available to those at the top.

Ms. Cutter added that Mr. Romney “continues to fail” the test of full disclosure by releasing only a summary of his earlier tax returns. But she said the 2011 return confirms “that he continues to profit from millions of dollars invested overseas.”