Q: If we calculate the time from the the birth of Jesus Christ, why is it that we do not calculate it from Christmas to Christmas, why from New Year to New Year? Or if this is not clear enough, than what is the difference between Christmas and New Year?
A: It has something to do with the solstice and the seasons and the time of jesus' birth. The week between christmas and New Year is like a grace period for our Spring to come around the same date.