OAKLAND, Calif. (RNS) Save the date: May 21, 2011.

If preacher Harold Camping is right, that’s the exact date Jesus will return and the righteous will fly up to heaven, leaving behind only their clothes.

That will be followed by five months of fire, brimstone and plagues, with millions of people dying each day and corpses piling in the streets. Finally, on Oct. 21, the world ends exactly as the Book of Revelation says it will — with a bottomless pit, a lake of fire and, at last, a new heaven and new earth.

Doomsday preachers come and go, but at nearly 90 years old, the spry Camping has managed to ignite a nationwide movement that has garnered national attention.

Camping is not an ordained pastor with a church, and has no formal religious training. He can’t read or speak Greek, Hebrew or Jesus’ native Aramaic. His main predictive tool rests by his side in his wood-paneled office that looks like it was borrowed from the set of AMC’s “Mad Men.”

“I made a very deliberate decision to make the Bible my university,” Camping said, reaching for his battered, brown King James Bible and flipping nimbly through pages with marked-up margins and taped-up tears.

“I bought a Bible with a good leather cover. This is the sixth one. When you use them all the time they wear out.”

The same can’t be said for Camping. Since the 1950s, he has broadcast his views via Family Radio, a global network of Christian stations where he now serves as unpaid president and primary on-air talent. His teachings air worldwide five nights a week via `Open Forum,’ a call-in show that draws listeners as far away as China and Ghana.

“Thank you for calling `Open Forum,”‘ Camping has said countless times in his trademark baritone, “and shall we take our next call, please?”

One of those callers is Chris McCann, an independent preacher who is part of a Philadelphia group of Camping followers that is spreading the word about May 21.

“God has put his stamp of approval that this is the day,” McCann said in a telephone interview. “I don’t doubt it, and I don’t look at the possibility of May 22 happening.”

Neither does Camping. Asked how he arrived at the date, he opened his Bible to Genesis and said Noah loaded animals into the ark in 4990 B.C., a number he said he arrived at years ago after looking at carbon dating, tree rings and other data. Paging forward to 2 Peter, he read aloud, “one day is with the Lord as a thousand years and a thousand years is one day.”

Leafing back to Genesis, he said that the seven days Noah spent loading the ark was really 7,000 years. He then added 7,000 to 4990 B.C to arrive at 2010. He added one more year, he said, because there is no year one in the Bible.

As for the exact date of May 21, he pointed again to Genesis, which says the flood began on the “17th day of the second month.” According to the Jewish calendar, which he believes God uses, that is May 21.

“Now I am telling you, that gets pretty heavy when you see this coming right out of the Bible,” he said, looking up from his Bible’s dog-eared pages.

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Camping finds further proof in the headlines: same-sex marriage, devastation in Japan, popular uprisings across the Arab world. They’re all divine warnings of the earthly obliteration to come.

“There are still people that God has to save, and he uses them to get them to cry out for his mercy,” Camping said.

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Camping is not the first to be enthralled with biblical numerology. In the 1500s, Scottish mathematician John Napier invented logarithms to better predict Jesus’ return. American farmer William Miller (the founder of Seventh-day Adventism) picked dates in 1843 and 1844. More recently, Chen Tao, a group based in Garland, Texas, predicted God’s return in the late 1990s.

A poll conducted last year by the Pew Research Center for the People & the Press found that 41 percent of Americans expect Jesus’ return before 2040. But pinpointing an exact date is unusual, said John R. Hall, a sociology professor and author of “Apocalypse,” an examination of doomsday groups.

“What is interesting is that (Camping) is claiming he is studying the Bible and this is what the Bible says,” Hall said. “That is a very different thing than saying God has spoken to me and this is what has been revealed. It leaves him quite a bit of wiggle room.”

Camping has wiggled before. He first predicted Jesus’ return in 1994 in a book named for that year — but with a big question mark at the end. While writing the book, he said the year 2011 began to come up in his calculations, but 1994 was more prominent.

When the year came and went, Camping explained that he was wrong and needed more study. “It just was a cudgel to keep studying,” he said.

Camping was once well-regarded in the evangelical community, both for his encyclopedic knowledge of Scripture and his radio empire. But in the late 1980s, when he began teaching that churches have strayed from the Bible and embraced false doctrine, he lost much of that support.

He announced his current prediction in his 2005 book, “Time Has an End,” and spreads the word through tracts, postcards and his radio shows. The final countdown has brought an international billboard campaign and a fleet of 20 decorated recreational vehicles that tour the country like movable billboards.

One set of RVs came to the University of Oregon, where Daniel Wojcik is a professor of folklore and author of “The End of the World As We Know It,” a study of end-times groups. Wojcik said prophets and their followers generally regroup after their prophesy fails, often recommitting themselves to the prophet.

“People try to rationalize it,” he said. “Often they say the end didn’t come, but a spiritual transformation took place, so the prediction was right on. Then there is the test-of-faith response, where they say, `Well, we weren’t ready for it.’ Or he (Camping) might just admit to being wrong.”

Asked about that, Camping does not hesitate.

“I do not even think about that possibility because I am trusting the Bible implicitly.”

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His followers, in turn, are trusting Camping. Allison Warden, a 29-year-old office manager in Raleigh, N.C., runs a website, WeCanKnow.com, dedicated to spreading news of Camping’s predictions. But what if he is wrong?

“It is a fair enough question,” she said. “But the fact that it is in Scripture is why you can say it with such a degree of certainty. It’s one of those things where you have to trust God.”