The answer
The Orthodox Churches use a specific formula so that the Feast of the Holy Resurrection always follows the Passover because the Crucifixion and Resurrection of Christ took place after He entered Jerusalem to celebrate the Passover. Western Churches' Easter celebration sometimes precedes the Passover by weeks. The main difference between the Eastern and Western Churches' celebration dates of the Holy Resurrection is based on their use of different calendars. The Western Churches use the Gregorian Calendar and the Orthodox Churches use the Julian Calendar.
You may also read, the following article on the Diocese website: The Date of the Glorious Feast of the Resurrection at http://www.suscopts.org/resources/literature/159/the-date-of-the-glorious-feast-of-the-resurrection/.
Answered by His Eminence Metropolitan Youssef (opens in a new tab)