The Orthodox Christian calendar for the year 2025 is a tool used by Orthodox Christians to determine the dates of religious (feasts) and fasts. It is based on the Julian calendar, which is 13 days behind the Gregorian calendar used in most of the world.
The Orthodox Church uses the Julian calendar because it was the calendar in use at the time of the First Council of Nicaea in 325 AD, which established the official doctrine of the Christian Church. The Gregorian calendar was introduced in 1582 by Pope Gregory XIII, but the Orthodox Church has never adopted it.
