Calendrical calculation

• The number of days between two dates.
• The date of a religious holiday, like Easter (the calculation is known as Computus) or Passover, for a given year.
• Converting a date between different calendars. For instance, dates in the Gregorian calendar can be converted to dates in the Islamic calendar with the Kuwaiti algorithm.
• Calculating the day of the week.

References

• Edward M. Reingold and Nachum Dershowitz. Calendrical Calculations. Cambridge University Press; 3 edition (December 10, 2007). ISBN 978-0521885409