exvigilare

For the Western Church the short answer is 35.

At the church’s (there was only one Christian Church then) first Ecumenical Council in 325, in Nicea (present-day Turkey), it was decided that Easter shall fall on the first Sunday following the first full moon following the spring equinox. So Easter can occur from March 22 to April 25 since the first Sunday after the first full moon after the spring equinox may occur as little as two or as many as 37 days from the equinox.

The calculations for the date of Easter are somewhat complicated. In the Western Church, Easter has not fallen on the earliest of the 35 possible dates, March 22, since 1818, and will not do so again until 2285. It will, however, fall on March 23 in 2008, but will not do so again until 2160. Easter last fell on the latest possible date, April 25, in 1943 and will next fall on that date in 2038. However, it will fall on April 24, just one day before this latest possible date, in 2011.

The cycle of Easter dates repeats after exactly 5,700,000 years, with April 19 being the most common date.

In 2008, the Western Church celebrates Easter on March 23. The Eastern Orthodox Church celebrates Pascha on April 27.