Easter is the movable holiday par excellence: its date, in fact, changes every year, always oscillating between March and April. In 2026, for example, April 5th falls: but have you ever wondered why?
It all depends on the first full moon of spring: Easter, in fact, falls on the Sunday following the first full moon that occurs after March 21st, the conventional date with which the spring equinox is indicated (even if, unlike what many think, the beginning of spring can occur between March 19th and 21st). In practice, this means that Easter can occur within a period of 35 days, ranging from March 22nd to April 25th.
In history, however, it has not always been like this: as also reported by Treccani, the rule in force today in the Catholic Church is the one established with the Gregorian reform of the calendar, desired by Pope Gregory XIII in 1582. Previously, however, Easter was calculated following complex rules established by the Julian calendar, which used the 19-year lunar cycle and the so-called “golden number” as reference, which assigned to each year the order number in the corresponding cycle nineteen year old.
The link between Easter and the lunar calendar depends on the fact that Christian Easter derives from Jewish Easter (or Pesach), established to commemorate the liberation of the Jewish people from slavery and the exodus from Egypt. Originally, in fact, Christian Easter was celebrated on the Sunday following the 14th of the month of Nisan, exactly like the Jewish one, but over the years the date became the subject of controversy since it did not always fall on a Sunday. In 325 the Council of Nicaea thus decided to separate the date of Christian Easter from the Jewish one, while continuing to calculate it based on the lunar cycles.
In any case, it should be noted that even today the full moon used to calculate the date of Easter does not correspond to the real astronomical one, but to the so-called “ecclesiastical full moon”, which is determined through a calculation system based on the epact – a number that indicates the age of the Moon on 1 January of each year – and on the Sunday letter, which identifies on which day of the week Sundays fall in a given year. The mechanism, therefore, is built to simplify the calculation and make it predictable well in advance, without having to wait for astronomical observations.
Once the date of Easter has been calculated, all the other movable feasts of the liturgical year are determined, from Carnival to Ash Wednesday, from Ascension to Pentecost.
