Perpetual Calendar

A perpetual calendar is a calendar valid for many years, usually designed to look up the day of the week for a given date in the future.

For the Gregorian and Julian calendars, a perpetual calendar typically consists of one of three general variations:

14 one-year calendars, plus a table to show which one-year calendar is to be used for any given year. These one-year calendars divide evenly into two sets of seven calendars: seven for each common year (year that does not have a February 29) with each of the seven starting on a different day of the week, and seven for each leap year, again with each one starting on a different day of the week, totaling fourteen. (See Dominical letter for one common naming scheme for the 14 calendars.)
Seven (31-day) one-month calendars (or seven each of 28–31 day month lengths, for a total of 28) and one or more tables to show which calendar is used for any given month.