The right-wing television personality announced what he called a long-planned break during his show on Tuesday, saying he would return on April 24 -- amid reports he may not come back.
Around this time of year, "I grab some vacation because it's spring and Easter time," the combative 67-year-old host said. "Last fall, I booked a trip that should be terrific."
His announcement follows a report in The New York Times last month saying the Fox cable news giant and O'Reilly had paid five women a total of $13 million in cases spanning 15 years, in exchange for their silence and agreement not to pursue litigation against Fox News, a favorite among conservatives.
The revelations come as "The O'Reilly Factor," US television's most-watched cable news show, is more popular than ever in its 20-year history.
Last week, the show averaged 3.7 million viewers over five nights, up 28 percent from the same week last year, according to Nielsen Research.
But O'Reilly's fate may come down to his station's bottom line.
Some 60 companies have said they would no longer advertise on his show following the Times report.
The time allotted for companies' advertisements on the show has been cut by more than half, according to an analysis released Tuesday by Kantar Media. Fox has filled the time with extra content.
That is adding to doubts about O'Reilly's future, with New York Magazine reporting sources inside the network as saying he may not return.
Although Fox News co-president Bill Shine wants the host to stay, the decision is up to the Murdoch family, which owns the network, the magazine said.
Fox News's parent company has said it will investigate the harassment claims.
Rotating substitute hosts will replace O'Reilly during his absence, Politico reported, with guest hosts already filling in for him during the show's Friday broadcasts for months.
Fox has chosen a woman to be the first host, Politico said: Dana Perino, former spokeswoman for president George W. Bush.
- 'A good person' -
Just last week, Trump -- reported to be an avid Fox News watcher -- came to O'Reilly's aid, calling him "a good person."
"Personally, I think he shouldn't have settled," the president said, suggesting O'Reilly should have fought the lawsuits against him in court.
O'Reilly himself did not directly deny any of the allegations, but said his prominence made him "vulnerable to lawsuits from individuals who want me to pay them to avoid negative publicity."
Last year, Trump defended former Fox News chief Roger Ailes, who stepped down in July amid sexual harassment accusations of his own.
Ailes, 76, had built the conservative news channel at the request of Rupert Murdoch, head of the media giant News Corp.
Accusations of sexual harassment also roiled Trump's election campaign last year following the release of a 2005 video that caught him on a "hot mike" making vulgar and degrading remarks about women and boasting about sexually assaulting them.
A dozen women came forward after the video's release to publicly accuse the Republican candidate of abusive behavior that, in some instances if confirmed, would have amounted to sexual assault.
Trump has consistently denied the accusations.
