Easter is not held on the same date every year. This is called a moveable feast. Currently all Christian Churches agree on how the date is calculated.

Easter is celebrated on the first Sunday following the first full moon which is on March 21st. This means it is celebrated in March or April. It can occur as early as March 22nd. And as late as April 25th.

Like the Roman Catholic Church use the Gregorian calendar. While Eastern churches like the Eastern Orthodox Church, use the Julian calendar.

Happy Easter.

More Info: en.wikipedia.org