In the Western Gregorian Calendar, the date of Easter Sunday is defined as the Sunday following the ecclesiastical Full Moon that falls on or next after March 21. While the pattern of dates so defined usually repeats each 19 years, there is a 0.08 day difference between the cycles. More accurately, the system has a period of 70 499 183 lunations which is about 5 700 000 years: more details are at astro.nmsu.edu/~lhuber/leaphist.html. This website also provides one version of an algorithm, attributed to Oudin, which is valid for any Gregorian year "y" to calculate the month "m" and day "dy" of Easter Day. In this article, the author shows how to manage a larger sample of dates by adapting the Oudin algorithm to a spreadsheet. With about forty calendars used in the World today, a study of cultural and religious dates often leads to interesting mathematical challenges.