LOS ANGELES (Reuters) - The evangelical Christian broadcaster whose much-ballyhooed Judgment Day prophecy went conspicuously unfulfilled on Saturday has a simple explanation for what went wrong -- he miscalculated.

Instead of the world physically coming to an end on May 21 with a great, cataclysmic earthquake, as he had predicted, Harold Camping, 89, said he now believes his forecast is playing out "spiritually," with the actual apocalypse set to occur five months later, on October 21.

Camping, who launched a doomsday countdown in which some followers spent their life's savings in anticipation of being swept into heaven, issued his correction during an appearance on his "Open Forum" radio show from Oakland, California.The headquarters of Camping's Family Radio network of 66 U.S. stations had been shuttered over the weekend with a sign on the door that read, "This Office is Closed. Sorry we missed you!"