Easter Sunday

Easter Sunday can fall on any one of the 35 days between March 22 and April 25. The actual date is the Sunday following the Paschal Full Moon (PFM) date for that year. The PFM dates were aligned with Pope Gregory XII's new calendar introduced in 1582 and the first "current" Easter calculations started in 1583.
This page calculates Easter for a specified year or range of years from the start of the Gregorian-calculated Easters up to 4099.
While not used to develop this page, the information here seems to provide a comprehensive description of the subject.