Calendar Wiki

This proposal does not change the existing Gregorian Calendar, but introduce an alternative representation which makes it easier to figure out the day of the week.

Each quarter has a fix number of 91 days except the final mini quarter which may have 1 or 2 days on leap day years. All years start on March 1st, which puts the leap day at the end of the year.


  • Jan 1st, 2000 becomes 1999-Q4-34
  • Feb 27th, 2000 becomes 1999-Q4-91
  • Feb 28th, 2000 becomes 1999-Q5-01
  • Feb 29th, 2000 becomes 1999-Q5-02
  • March 1st, 2000 becomes 2000-Q1-01
  • April 1st, 2000 becomes 2000-Q1-32
  • May 31st, 2000 becomes 2000-Q2-01
  • September 1st, 2000 becomes 2000-Q3-03
  • December 31st, 2000 becomes 2000-Q4-33


  • Modulo 7 of day of quarter (DoQ) maps to day of week constantly throughout the year (but varies from year to year). E.g. if Q1-01 this year is Monday then Q2-08, Q3-78, Q4-85, etc are all Monday.
  • Modulo 30 of DoQ maps to day of pseudo month of 30,30,31 each quarter.
  • Maximum of 91 instead of 366 (ordinal date format) for modulo operation which is not too hard for mental calculation.
  • Each date in the Gregorian calendar has a corresponding date in this proposal, most holidays remains the same.
  • Does not rely on Gregorian calendar to determine when to start a year like ISO weekly calendar.
  • Shorter digit string needed to represent the date compared to most monthly calendars. E.g. November 31st is represented with (Q)3-91 rather than 11-28.


  • Not as straight forward as other weekly calendars when it comes to figuring out the day of the week.
  • Additional mini quarter, Q5.
  • The first two months of the (month-based) year belong to the previous (quarter-based) year, thus the majority of days of that quarter belong to the later year but it itself belongs to the earlier year. This is incompatible with established ISO 8601 rules, e.g. regarding the first and last week of the year.

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