Editor's note: Part of the CNN Republican debate fact-checking series
(CNN) -- During Monday's Republican presidential debate, former Massachusetts Gov. Mitt Romney said he probably would release a tax return in April -- though he declined to commit -- asserting that recent GOP nominees waited until tax season in election years.
Romney's statement about his tax return came after Texas Gov. Rick Perry pushed him to release his tax information, saying his was already out.
"Mitt, we need for you to release your income tax so the people of this country can see how you made your money, and I think that's a fair thing," Perry said, during the Fox News-Wall Street Journal Republican presidential debate in Myrtle Beach, South Carolina. "Listen ... as Republicans, we cannot fire our nominee in September. We need to know now. So I hope you'll put your tax records out there this week so the people of South Carolina can take a look and decide if we've got a flawed candidate or not."
The statement: "You know, I looked at what has been done in campaigns in the past with Sen. McCain and President George W. Bush and others. They have tended to release tax records in April or tax season. I hadn't planned on releasing tax records because the law requires us to release all of our assets, all the things we own. That I have already released. It's a pretty full disclosure. But, you know, if that's been the tradition and I'm not opposed to doing that, time will tell. ... I sort of feel like we are showing a lot of exposure at this point. And if I become our nominee, and what's happened in history is people have released them in about April of the coming year, and that's probably what I would do."
-- Former Massachusetts Gov. Mitt Romney
The facts: A presidential candidate is not required by election law to disclose tax returns, though most voluntarily do. During the 2008 GOP presidential battle, Romney did not release a tax return.
Of the candidates who do release them, a few do so relatively early in the year. Former House Speaker Newt Gingrich, who, like Perry, has been pushing Romney to release his returns, has said he would release his own on Thursday, two days before the South Carolina primary.
In 2008, Sen. John McCain released his tax information in mid-April, by which time he had virtually wrapped up the GOP nomination. Sen. Barack Obama released his 2000-2006 tax returns in late March; his main rival, Sen. Hillary Clinton, released hers in mid-April.
Sen. John Kerry, who won the Democratic nomination in 2004 also released his in mid-April. By this time, President George W. Bush was releasing his information yearly, as presidents generally do.
In mid-April 2000, Bush's campaign released figures for his earnings and the amount he paid in taxes in 1999, but didn't have his tax return at the time, because the blind trust that was responsible for the return needed to file for an extension.
In 1996, eventual GOP nominee Sen. Bob Dole released tax returns in January.
The verdict: True. McCain and George W. Bush released their tax information in April of the first year they became their party's nominee.
CNN's Jason Hanna and Lindsey Knight contributed to this report.