Netogram.com^v2.0

Easter and the holidays that are related to it are moveable feasts, in that they do not fall on a fixed date in the Gregorian or Julian calendars (both of which follow the cycle of the sun and the seasons). Instead, the date for Easter is determined on a lunisolar calendar similar to the Hebrew calendar. The First Council of Nicaea (325) established the date of Easter as the first Sunday after the full moon (the Paschal Full Moon) following the northern hemisphere's vernal equinox. Ecclesiastically, the equinox is reckoned to be on March 21 (even though the equinox occurs, astronomically speaking, on March 20 in most years), and the "Full Moon" is not necessarily the astronomically correct date.

In Western Christianity, using the Gregorian calendar, Easter always falls on a Sunday between March 22 and April 25, inclusively. The following day, Easter Monday, is a legal holiday in many countries with predominantly Christian traditions. Eastern Christianity bases its calculations on the Julian Calendar. Due to the 13 day difference between the calendars between 1900 and 2099, March 21 corresponds, during the 21st century, to the 3rd of April in the Gregorian Calendar. Easter therefore varies between April 4 and May 8 on the Gregorian calendar (The Julian calendar is no longer used as the civil calendar of the countries where Eastern Christian traditions predominate). Among the Oriental Orthodox some churches have changed from the Julian to the Gregorian calendar and the date for Easter as for other fixed and moveable feasts is the same as in the Western church (source: wikipedia.org)