Harold Camping lets out a hearty chuckle when he considers the people who believe the world

"That date has not one stitch of biblical authority," Camping says from the Oakland office where he runs Family Radio, an evangelical station that reaches listeners around the world. "It's like a fairy tale."

The real date for the end of times, he says, is in 2011.

This is not the first time Camping has made a bold prediction about Judgment Day.

On Sept. 6, 1994, dozens of Camping's believers gathered inside Alameda's Veterans Memorial Building to await the return of Christ, an event Camping had promised for two years. Followers dressed children in their Sunday best and held Bibles open-faced toward heaven.

But the world did not end. Camping allowed that he may have made a mathematical error.

The number 5, Camping concluded, equals "atonement." Ten is "completeness." Seventeen means "heaven." Camping patiently explained how he reached his conclusion for May 21, 2011.

"Christ hung on the cross April 1, 33 A.D.," he began. "Now go to April 1 of 2011 A.D., and that's 1,978 years."

Camping then multiplied 1,978 by 365.2422 days - the number of days in each solar year, not to be confused with a calendar year.

Next, Camping noted that April 1 to May 21 encompasses 51 days. Add 51 to the sum of previous multiplication total, and it equals 722,500.

Camping realized that (5 x 10 x 17) x (5 x 10 x 17) = 722,500.

Or put into words: (Atonement x Completeness x Heaven), squared.

"Five times 10 times 17 is telling you a story," Camping said. "It's the story from the time Christ made payment for your sins until you're completely saved.

"I tell ya, I just about fell off my chair when I realized that," Camping said.