Calendar Wiki

The Truncated Dee-Cecil Calendar is a variation of the calendar with the 33-year leap day cycle proposed by William Cecil.  In this version by Walter Ziobro, the 33-year leap day cycle would continue for 12 cycles of 396 years, after which there would be one four-year olympiad, for a total of 400 years. The 33-year cycles would then recommence in the next year.


There are 3 advantages of such a calendar:

  1.   The 33-year leap day cycle would cause less jitter of the equinox and solstice dates.
  2. The application of ISO 8601 rules to such a calendar would cause the 53rd week of the week numbering scheme to be more smoothly distributed over the 400 year period.  This could also make concurrence with leap-week calendars more symmetrical.
  3.   The 400-year cycle would have 146,097 days, or 20,871 weeks, exactly the same as the current Gregorian Calendar, which would assist, either in conversion from one calendar to the other, or in date-to-date mapping, if both calendars run concurrently.


Currently, both the Gregorian and the Truncated Dee-Cecil Calendar have the same calendar dates.  This is so because the 33-year cycle recommenced in 2001, and both calendars will have the same dates until 2036, which will be a leap year in the Gregorian Calendar, but not the Truncated Dee-Cecil Calendar.  Thus, it would be possible to convert from the Gregorian Calendar to the Truncated Dee-Cecil Calendar at any time from now until 2036 without adjusting any dates.

However, if the calendar in not converted by then, both calendars could run concurrently.  To minimize any confusion, alternative month names can be used for the Truncated Dee-Cecil Calendar.  Since Dee and Cecil were both Englishmen, English names for the alternative months seem appropriate. So, the alternative month names for the corresponding Gregorian month names could be:

Gregorian to Truncated Dee-Cecil (abbreviations in parentheses)
Classic Unambiguous Length
January Newmonth (Nmt) 31 days
February Shortmonth (Smt) 28/29 days
March Firstmonth (1mt) 31 days
April Secondmoth (2mt) 30 days
May Thirdmonth (3mt) 31 days
June Fourthmonth (4mt) 30 days
July Fifthmonth (5mt) 31 days
August Sixthmonth (6mt) 31 days
September Seventhmonth (7mt) 30 days
October Eighthmonth (8mt) 31 days
November Ninthmonth (9mt) 30 days
December Tenthmonth (Tmt) 31 days6

As the Truncated Dee-Cecil Calendar would have the same number of days as the Gregorian Calendar in 400 years, 146,097 days, it would have exactly one day more than the Revised Julian Calendar in 3,600 years (1,314,873 days, compared to 1,314,872 days of the Revised Julian Calendar), and it would also have exactly one day more than the uninterrupted Dee-Cecil Calendar in 13,200 years (4,821,201 days, compared to 4,821,200 days of the uninterrupted Dee-Cecil Calendar). Additionally, it would have one day more than the Amended Julian Worldwide Calendar (or any other calendar which drops one day from the Julian Calendar in 128 years), in 3,200 years (1,168,776 days, as compared to 1,168,775 days).