As you may have learned from one of the 2,000 billboards worldwide, May 21, 2011, is Judgment Day, upon which the righteous – which totals 3 percent of humanity – will be whisked away to the sweet hereafter, leaving the rest of us to weather five months of extreme natural disasters until Oct. 21, whereupon God destroys the entire universe and everyone left in it.

At least that's what Harold Camping says. The head of Family Radio broadcasting network, which boasts 150 outlets in the United States, has what his website calls "infallible, absolute proof" that there's no point in making plans for Memorial Day weekend. It goes like this:

Camping says that because Jesus was crucified on Friday, April 1, 33 AD, and that it takes exactly 365.2422 days for the earth to complete one orbit of the sun, we can conclude that, on April 1, 2011, Jesus was crucified exactly 722,449.07 days ago. Add 51 days to this to get to May 1, and you get a figure of 722,500.07.

Round that down to the nearest integer, and you get 722,500, which is an important number because it is the square of 5 x 17 x 10 . The number five, says Camping, represents atonement. Ten represents completeness, and 17 represents heaven. Multiply all these together – twice – and you get 722,500. Therefore the apocalypse kicks off on Saturday, May 21.

Skeptics of Camping's method might ask why the date of the end of the world is linked to that of Jesus' crucifixion, why the numbers five, 10, and 17 represent what Camping claims they represent, why they should be multiplied together, why they should then be squared, and, for that matter, why the Bible would contain esoteric numerological references predicting the end of the world in the first place. They could also point out that April 1, 33 AD was actually a Wednesday, and that, under Camping's method, April 1, 2011 gets counted twice.

Others use different methods to calculate the last day. For example, Dec. 21, 2012 marks the end of the 5,125-year-long cycle in the Mesoamerican Long Count calendar, leading some people – particularly those who believe that the dating systems of pre-Columbian Americans can predict events hundreds of years in the future – to believe that the world will end on that date.