The Eastern Orthodox Church calculates the date of Easter differently, so the Eastern Orthodox celebration of Ascension will usually be after the western observance (either one week, or four weeks, or five weeks later; but occasionally on the same day). The earliest possible date for the feast is May 13 (of the western calendar), and the latest possible date is June 16. Some of the Oriental Orthodox Churches, however, observe Ascension on the same date as the Western Churches.