5,700,000 years

Did you notice the full moon?

The actual calculations for the date of Easter are somewhat complicated, but can be described briefly as follows:

Easter is determined on the basis of lunisolar cycles. The lunar year consists of 30-day and 29-day lunar months, generally alternating, with an embolismic month added periodically to bring the lunar cycle into line with the solar cycle. In each solar year (January 1 to December 31), the lunar month beginning with an ecclesiastical new moon falling in the 29-day period from March 8 to April 5 inclusive is designated as the Paschal lunar month for that year. Easter is the 3rd Sunday in the Paschal lunar month, or, in other words, the Sunday after the Paschal lunar month's 14th day. The 14th of the Paschal lunar month is designated by convention as the Paschal full moon, although the 14th of the lunar month may differ from the date of the astronomical full moon by up to two days. Since the ecclesiastical new moon falls on a date from March 8 to April 5 inclusive, the Paschal full moon (the 14th of that lunar month) must fall on a date from March 21 to April 18 inclusive.

Accordingly, Gregorian Easter can fall on 35 possible dates - between March 22 and April 25 inclusive. It last fell on March 22 in 1818, and will not do so again until 2285. It fell 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, happening 220,400 times or 3.9%, compared to the median for all dates of 189,525 times or 3.3%.