Newt Gingrich and his wife, Callista, paid nearly $995,000 in federal taxes on adjusted income of $3.14 million in 2010, translating to an effective tax rate of about 31.6 percent, according to tax documents released by his presidential campaign late Thursday.

The records appear to put the Gingriches in line with the typical tax rate for people earning their level of income, which ranks them in the top 1 percent of all taxpayers. But the percentage is nearly double the rate that Republican rival Mitt Romney estimates paying on his earnings, most of which count as capital gains and are taxed at 15 percent.

The Gingriches reported $450,245 in combined wages, plus $2.53 million in income from partnerships and S corporations that are part of the former House speaker’s financial empire, often dubbed Newt Inc. The couple also reported about $66,000 from speaker’s and director’s fees, rental income and dividends, and said they donated $81,133 to charities.

The pair reported $4,184 in net short-term capital gains and $32,541 in net long-term capital losses. The campaign also released a copy of the 2010 tax return for the Gingrich Foundation, which gave $120,000 to charitable causes, including the Basilica of the National Shrine of the Immaculate Conception.

Gingrich said this week that he will release his 2011 returns when they are ready. He has not indicated whether he will release more. Many recent presidential candidates, including Barack Obama, have released tax returns for multiple years during their campaigns.

Gingrich’s release was aimed squarely at ratcheting up the pressure on Romney, who is worth an estimated $250 million and has faced growing questions during the GOP primaries about his wealth and tax status. After first resisting, Romney said this week that he will release his personal tax forms in April.

The lower rate for capital gains, which includes profits from the sale of stocks, bonds and real estate, has been central to a months-long debate between Republicans and Democrats over whether to raise taxes on the wealthy to help lower the federal deficit.

Texas Gov. Rick Perry, who dropped out of the GOP race Thursday, as well as Gingrich and former senator Rick Santorum (Pa.), have pressed Romney to release his returns now to give primary voters a chance to review them. House Democrats also started a petition drive Thursday “telling Mitt Romney to release his tax returns.”

Gingrich said this week that his “goal was not to raise Mitt Romney’s taxes,” but rather to push his own proposal for an “optional” 15 percent rate for all taxpayers.

The persistent questions about Romney’s wealth and investment strategies, including his use of offshore accounts and his tenure at the Bain Capital private equity firm, have put the former Massachusetts governor on the defensive in the days before Saturday’s pivotal South Carolina primary.

Obama and his wife, Michelle, reported $1.7 million in adjusted gross income in 2010, most of it coming from sales of two books Obama wrote before winning the White House, according to the couple’s most recent tax returns. The Obamas donated about 14 percent of their gross income to charity.