When it comes to their federal taxes in the last two years, Republican presidential candidate Mitt Romney has paid a lower federal tax rate than his running mate, Rep. Paul Ryan.

Ryan, R-Wis., paid an effective federal tax rate of 15.9 percent in 2010 and 20 percent in 2011, according to tax returns released by the Romney campaign Friday evening.

In 2010, Ryan and his wife reported an adjusted gross income of just over $215,000. Most of that came from Ryan's congressional salary. They paid more than $34,000 in federal taxes on that income. They also paid $3,168 in employment taxes for a household worker.

In 2011, the couple reported an adjusted gross income of more than $323,000 and paid nearly $65,000 in federal taxes. In addition to Ryan's salary, the couple made more than $50,000 in investment income from capital gains and qualified dividends. They also made more than $116,000 in rental income, royalties and trust income. The couple owns rental property in Oklahoma, according to the return.

Ryan reported $2,600 in charitable donations in 2010 and nearly $13,000 in donations in 2011. The Romney campaign said the Ryans' charitable contributions have gone to groups such as the Boy Scouts of America, Junior Achievement, Women & Children's Horizons, which helps victims of sexual abuse and domestic violence, and Care Net, which counsels women who have unplanned pregnancies to seek alternatives to abortion.

Romney's tax returns have become a distraction for his campaign, with Democrats and even some fellow Republicans urging Romney to release more than two years of his returns. Senate Majority Leader Harry Reid, D-Nev., reignited the debate by making an unsubstantiated claim _ roundly criticized _ that Romney had not paid any taxes for 10 years.

Romney said Thursday he has paid at least 13 percent of his income in federal taxes in each of the past 10 years. But he has refused to release more of his returns, calling the fascination with his taxes "small-minded." He has released his 2010 returns and a preliminary 2011 return.

Romney paid about $3 million in federal income taxes in 2010 for an effective federal tax rate of 13.9 percent. For 2011, Romney's campaign estimates that he will pay about $3.2 million for an effective federal tax rate of 15.4 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 the nonpartisan Joint Committee on Taxation. By comparison, Romney made about $21 million a year in 2010 and 2011.

Romney is able to keep his tax rate low because most of his income is from investments, which are generally taxed at a lower rate than wages.

President Barack Obama and his wife reported paying $162,074 in federal taxes last year on $789,674 in adjusted gross income, for an effective tax rate of 20.5 percent.