Easter is determined each year as the first Sunday after the Paschal Full Moon, which is the first full moon on or after the fixed date of March 21, the Church's approximation of the spring equinox. If the full moon falls on a Sunday, Easter is celebrated the following Sunday
. This calculation is based on a lunisolar calendar system, combining the solar year (marked by the equinox) and the lunar month (marked by the full moon). The Paschal Full Moon is not the actual astronomical full moon but a mathematically approximated date following a 19-year Metonic cycle
. The reason for this method dates back to the Council of Nicaea in 325 AD, aiming to standardize Easter's date independently from the Jewish calendar and to tie it to the spring season and lunar cycles
. Because of differences between the Julian calendar (used by many Eastern Orthodox churches) and the Gregorian calendar (used by Western Christian churches), Easter often falls on different dates in these traditions
. In summary:
- Easter = first Sunday after the Paschal Full Moon on or after March 21.
- Paschal Full Moon = ecclesiastical full moon, a calculated date, not the exact astronomical full moon.
- March 21 = fixed date for the spring equinox in the Church calendar.
- If the full moon is on a Sunday, Easter is the next Sunday.
- Different Christian traditions may use different calendars, causing date variations.
This system ensures Easter falls between March 22 and April 25 each year
Example for 2025:
- Spring equinox: March 20 (astronomical), March 21 (ecclesiastical)
- Paschal Full Moon: April 12
- First Sunday after April 12 is April 20, so Easter 2025 is April 20
