Mitt Romney’s presidential campaign is releasing a brief summary of 20 years of tax returns on Friday, and his accountant says it will show he gave 13.45 percent of his adjusted gross income to charities.

That’s nearly twice the rate of President Obama, who according to his tax returns from 2000 through 2011 donated just less than 7 percent of his adjusted gross income to charities.

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Mr. Romney’s campaign did not release his returns, but instead had his trustee, Brad Malt, write a blog post giving some details of returns from 1990 through 2009.

The campaign has released Mr. Romney’s 2010 return and, later Friday, will release his 2011 return, which he filed with the IRS earlier in the day.

That return will show Mr. Romney and his wife Ann paid $1.9 million in taxes on income of $13.7 million, for a rate of 14.1 percent, Mr. Malt said. Most of that income is from investments, which are usually taxed at a lower rate than salary or wages.

Mr. Malt said the Romneys would have had an even lower tax burden if they’d claimed the full deduction for all of their charitable giving in 2011, but said they “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.”

When charitable contributions and federal and state taxes are combined, it amounted to 38.5 percent of the Romneys’ income, the trustee said.

Mr. Malt said the Romneys have owed taxes in each of the years in question — which contradicts a charge Senate Majority Leader Harry Reid, Nevada Democrat, issued earlier this summer.