Calendar Years Repeat Themselves
There are 14 possible Gregorian calendars
Years that share the same amount of days and that start on the same day of the week will have the same monthly calendar grids. There are only 14 possible calendar grid patterns. Most calendar years will repeat themselves every 6, 11, or 28 years. For example, this little gem of a postcard calendar from 2006 can also be used next year, in 2023. The last time it was able to be reused was in 2017, and after next year, if we store it in a safe place, we can use it again in 2034. Leap years have the longest amount of time before reuse is possible, averaging 28 years between repeating calendar grids.
Fonte: https://www.asgardpress.com/reuse-a-calendar/?utm_source=chatgpt.com
There are 14 possible Gregorian calendars, given that a Gregorian year can begin on any day of the week and have either 365 or 366 days. In this post I'm going to explore how often each of those calendars can be reused.
Leap years begin on all seven days of the week, starting two days earlier in the week than the previous leap year. Thus, a 366-day calendar can only be reused once every 28 years:
https://blog.dbinfo.app.br/images/Screenshot_at_2026-08-02_15-35-36.png
Leap years begin two days of the week earlier than the previous leap year, so leap year calendars can be reused every 28 years.
365-day calendars recur more frequently, but because of the insertion of leap years, not quite so regularly. This year's calendar started on Saturday, as did 2011's calendar, and before that 2005's. In general, non-leap year calendars recur after either 6 or 11 years: after 6 years for years immediately following a leap year, after 11 years for other non-leap years. That means a non-leap calendar recurs after 6 years, then after 11 years, then after another 11 years, then after 6 years again, repeating in what, like leap-calendar recurrence, is a 28-year cycle.
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Calendars for non-leap years can be reused after either 6 or 11 years, depending on where they fall in the 4-year leap year cycle.
Fonte: https://blog.exupero.org/calendar-recurrence/?utm_source=chatgpt.com
