Although Easter is a most important day of the year in many religions, most people do not understand why the date of Easter changes from year to year or how the date is determined. We all know that we can count on Easter to fall on a Sunday sometime in late March through sometime in April, but how the particular Sunday of Easter in any particular year is determined has been an on-going mystery for many people.
Religions that follow the Gregorian calendar, like here in the United States, celebrate Easter on the first Sunday following the Vernal Equinox after the occurrence of a full moon. I will attempt to simplify that explanation. The Vernal Equinox, also known as the First Day of Spring, generally falls on March 21st. Next you must follow the cycles of the moon to know when the next full moon will occur after the Vernal Equinox has occurred. Once the full moon has occurred, Easter will be set on the very next Sunday immediately following. Therefore, Easter will never occur earlier than March 22nd, the day after the Vernal Equinox IF it also happens to be on a Saturday with a full moon, or any later than April 25th.
So, that is how the floating feast of Easter is calculated from year to year. If you are still thoroughly confused, you can always continue to rely on a calendar to let you know on which Sunday in March or April Easter will be celebrated on!