"Pedantry incoming: The Jesus birthday assumption is invalid and has known to be so for a long time. Based on when Herod lived and died, Jesus would have been born probably no later than 4 BC, especially considering the tale of the Massacre of the Innocents predates that of the gospel books. Also, AD is the calendar *era*, and while the standard one for the west, is only one of many competing eras. Our calendar is the Gregorian calendar, and again there are multiple competing calendars (which is why Ramadan, for example, keeps shifting through the year)." - Chris Charabaruk