Republican presidential nominee Mitt Romney paid \$1.9m (£1.1m) in taxes on income of \$13.6m (£8.3m) in 2011, an effective rate of 14.1%.
Accountants PwC also released a letter covering Mr Romney and his wife Ann's filings from 1990 to 2009.
It backed up the candidate's claim on the campaign trail that he had never paid less than 13% in tax.
It said the Romneys' average annual effective federal tax rate was 20.2% over the 20-year period, with the lowest rate being 13.7%.
Mr Romney, the former governor of Massachusetts and a multi-millionaire former private equity investor, has faced severe criticism throughout the race for refusing to release more tax data.
He released his 2010 tax returns, and promised he would do the same with 2011 before his October filing deadline, but he has repeatedly stressed he was not likely to release full tax data for years prior to 2010.
Mr Romney's critics say he should follow the example of his father, former Michigan Governor George Romney, who released 12 years of tax returns during his own unsuccessful run for president in 1968.
Brad Malt, the trustee of the Romneys' blind trust, said in a blog post that the Romneys donated \$4,020,772 to charity in 2011, amounting to nearly 30% of their income.
"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," Mr Malt added.
Mr Romney has previously said he would not be qualified to be president if he paid more taxes than were required.
"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 told ABC News in July.
The majority of Mr Romney's income comes in the form of dividends and capital gains, which are taxed at a lower rate than ordinary income.
US Political Analyst Jon-Christopher Bua said: "In politics timing is everything. After two of the worst weeks in his campaign it seems like the perfect time for Romney to get all the bad news out at once by releasing these tax returns.
"As suspected these returns contain more fodder for his opposition.
"With six weeks remaining, Romney needs to refocus his campaign and deliver a smashing performance during the October3rd first debate with Barack Obama, or it could be curtains for Mitt."
