Mitt Romney's presidential campaign released his 2011 tax returns Friday afternoon, revealing that the Republican presidential candidate deliberately paid more in federal income taxes last year.

Brad Malt, the trustee of Romney's blind trust, explains in a campaign blog post that on their 2011 returns, the Romneys artificially kept their tax rate above 13 percent by claiming deductions for just over half of their $4 million charitable donation.

Romney has previously said that he never paid less than 13 percent on his federal income taxes.

Malt writes:

"The Romneys’ generous charitable donations in 2011 would have significantly reduced their tax obligation for the year. 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% in income taxes in each of the last 10 years."

But Romney could still opt to recoup the money sometime in the future. Tax experts told Business Insider Friday that Romney can amend his returns any time within the next three years, and request the full deduction from the U.S. government.

Romney, who filed for an extension on his 2011 returns, said in April that he would release the returns after they were finalized and submitted to the IRS. He released his 2010 tax returns earlier this year, but has said he will not release any additional years of returns.

The campaign does appear to have made a concession on that front however. Along with the candidate's 2011 tax returns, the campaign has posted a letter from Romneys tax preparer, PriceWaterhouseCoopers, summarizing Romney's tax rates from 1990 to 2009.

The letter claims that Romney's average federal income tax rate over those 20 years was 20.20%; that the lowest rate Romney paid was 13.66%; and that there were no years during which Romney did not owe both federal and state income taxes.

Romney and his running mate Paul Ryan also released letters from physicians, declaring the candidates to be in preternaturally good health.

You can check out all of the new docs here >

*This post has been updated