The Gregorian Calendar is currently the most widely useful civil calendar. It is named after pope Gregory XIII, who introduced the calendar in 1582. The calendar was a refinement after the Julian Calendar. The motivation to the reform was to stop drift of the calendar in respect of the equinox and solistices. Since 1582 the Gregorian Calendar has been adopted in many countries. Due to calendar seasonal error a 1 day drift of the calendar will occur after 3030 years.
The 400 years Gregorian Calendar cycle contains 303 common years and 97 leap years.
Nowadays the most popular are digital calendars, hovewer it's good to look into the traditional version of the Gregorian Calendar.
I prepared a couple of long term calendars on the 1601-4000 period. I shown the way to compute the days and weeks also. All of my long term calendars includes easter dates. In order to use a ready prepared Easter dates I referred to The GM arts website, where Easter up to 4000 year is provided.