Unlike Christmas Day, Easter - as celebrated by Western Christians - can occur on any date in a 5 week period from late March to late April. This is because it's defined as the first Sunday after the first full moon after the Spring Equinox and, of course, the lunar month doesn’t follow the months as defined in the Gregorian Calendar.
To complicate things further, Eastern Orthodox churches tend to have their Easter later than Western Christians. They use the Julian Calendar which differs from the Gregorian Calendar by 13 days. They also observe the Nicene tradition of not celebrating Easter until after the Jewish Passover to maintain the sequence of events of Jesus's crucifixion.
All that may be about to change with discussions taking place between the various Christian churches with a view to fixing Easter in the first couple of weeks of April. It would never be set to a particular date like December 25th; to be meaningful, it needs to be on a Sunday. Nevertheless, it would mean that a whole range of Church feasts (such as Ash Wednesday, Holy Thursday, Good Friday, Ascension Thursday and Pentecost Sunday) would be falling within a much narrower time range than before.
The original suggestion came from the Coptic Church in Egypt. Pope Tawadros II proposed it to the Roman Catholic Church last year. Pope Francis signalled his agreement and now it seems that the Anglican Communion is coming on board too. The Russian Orthodox Church seems open to the idea - albeit with the caveat that the date be determined according to the Orthodox calendar. Whether this means simply that it should always be after the Passover is unclear at this stage.
But…..they’re all talking and seemingly agreeing and that can only be a good thing.
Easter date could be fixed 'within five to 10 years' - Independent.ie
Easter Fixed Date? Catholic And Orthodox Churches Could Celebrate On Same Sunday By 2021
Archbishop of Canterbury working with Pope to establish common Easter date for all Christians