While the Gregorian Calendar has the advantages of wide use, internal stability, and a relatively simple and reasonably accurate leap-year rule, it has some features which are inconvenient. Among those are the irregular lengths of the months. This is the inheritance of the judgement of Julius Ceasar, who set the lengths of the months of the calendar to suit his purposes. Those purposes, however useful at the time, have been lost to us.   

Attempts to adjust the lengths of the months to a more convenient form have stalled over disagreements of what should be the basis of such reordering. Should the months have alternating lengths? Should they commence every quarter on the same weekday? Wouldn’t changing the lengths of the months cause confusion among people trying to ascertain their correct birthdays, anniversaries and holidays?   

A proposal by Walter Ziobro is cited here. Rather than change the lengths of the months as we know them, this proposal keeps the current months as they are, and runs two parallel calendars, with different names to reflect the different schemes. All the old dates remain in the old months, and can be uniquely identified with the dates in the alternate months. Thus, no one’s birthday, anniversary, or holiday is “lost”.  

Under this proposal, the New Year starts on the same day as in the current Gregorian Calendar, the unbroken seven-day week is maintained, and the current leap-year rule is kept. What changes are the relative lengths of the alternate months.   

Two alternate month calendars are offered. The first, called the Mostly Alternating Month Length Calendar, alternates the lengths of the months according to the sequence 30-30(31 in ly)-30-31-30-31-30-31-30-31-30-31. The second, called the Mostly Same Weekday Quarter Start calendar, sets the lengths of the months according to the sequence 31-30(31 in ly)-30-31-30-30-31-30-30-31-30-31, which causes the start dates of every third month to fall on the same day of the week in every common year, and in the last nine months of any leap year.

The names of the alternate months are based on Latin ordinal numbers in a style similar to the names of the last four months of the current Gregorian year, which last four months are, coincidentally, the same in both the Gregorian and the two alternate calendars. Thus Christmas is on December 25 in all three, in case you were wondering. Long form versions of the names include the letters in parentheses. Unique three-letter abbreviations are also shown. The Gregorian date of the first of each alternate month is given:

Current Gregorian Alternating Month Lengths Mostly Same Weekday Quarter Start
January (Jan) 31 days Unde(ce)mber (Unr) 30 days Jan 1 Undecil(is) (Unl) 31 days Jan 1
February (Feb) 28/29ds  Duode(ce)mber (Dur) 30/31ds Jan 31  Duodecil(is) (Dul) 30/31ds Feb1
March (Mar) 31 days  Primember (Prr) 30 days Mar 2  Primil(is) (Prl) 30 days Mar 3
April (Apr) 30 days  Secundember (Scr) 31 days Apr 1 Secundil(is) (Scl) 31 days Apr 2
May (Mai)  31 days  Tertember (Trr) 30 days Mai 2  Tertil(is) (Trl) 30 days Mai 3
June (Jun) 30 days  Quartember (Qrr) 31 days Jun 1 Quartil(is) (Qrl) 30 days Jun 2
July (Jul) 31 days  Quintember  (Qnr) 30 days Jul 2  Quntil(is) (Qnl) 31 days Jul 2
August (Aug) 31 days  Sextember (Sxr) 31 days Aug 1 Sextil(is) (Sxl) 30 days Aug 2
September (Sep) 30 days  Same as current Gregorian
October (Oct) 31 days  Same as current Gregorian
November (Nov) 30 days Same as current Gregorian
December (Dec) 31 days Same as current Gregorian 

Coincidentally, Undecil(is) is identical to January, and Sextember is identical to August, so the current Gregorian name may be substituted for either. 

Ziobro states his indebtedness to Karl Parlmen, who provided useful feedback on his proposals. 

See also