Easter most generally falls on the first Sunday after the first full moon occurring on or after the vernal equinox. The 2018 equinox came on March 20, marking an unofficial beginning of spring for the Northern Hemisphere. The first full moon after the March equinox comes on Saturday, March 31. Voila. In 2018, Easter Sunday is the following day, April 1.
The Council of Nicaea – first ecumenical council of the Christian church – established the date of Easter when it met in Turkey in the year 325 CE. By ecclesiastical rules set centuries ago, there are 35 dates on which Easter can take place. The earliest possible date for Easter is March 22 and the latest possible date is April 25.
2018 doesn’t hold a record for the earliest possible Easter. The earliest Easter in the 21st century came in the year 2008 (March 23, 2008). Another March 23 Easter won’t come again until the year 2160.
The last time Easter fell on March 22 (earliest possible date) was in 1818, and the next time will be in 2285. The most recent time an Easter came in March was March 27, 2016.
The century’s latest Easter will occur in the year 2038 (April 25, 2038). After that, it will next fall on April 25 in the year 2190.
More dates at http://tlarsen2.tripod.com/thomaslarsen/easterdates.html
Easter can never come as early as March 21 because, by ecclesiastical rules, the vernal equinox is fixed on March 21. That’s in spite of the fact that in the 21st century (2001 to 2100) every March equinox after the year 2007 will fall on March 19 or March 20.
Moreover, an ecclesiastical full moon does not necessarily happen on the same date as an astronomical full moon. Therefore, it’s possible for an ecclesiastical Easter and an astronomical Easter to occur on different dates, as well.
Next year, in 2019, the full moon will come on March 21, 2019 (after the spring equinox). Yet, the ecclesiastical Easter will fall on April 21, 2019, whereas the astronomical Easter will take place March 24, 2019.
Bottom line: How the date of Easter is determined, and some dates of earliest and latest Easters. Happy Easter to all who celebrate it!
Bruce McClure has served as lead writer for EarthSky's popular Tonight pages since 2004. He's a sundial aficionado, whose love for the heavens has taken him to Lake Titicaca in Bolivia and sailing in the North Atlantic, where he earned his celestial navigation certificate through the School of Ocean Sailing and Navigation. He also writes and hosts public astronomy programs and planetarium programs in and around his home in upstate New York.