Calendar Wiki

This page lists alternate month names for use with leap week calendars which start the 7-day week on Sunday, such as the original Hanke-Henry Permanent Calendar (HHPC) and the World Calendar with Leap Weeks (WCLW).


Dr. Dick Henry of John Hopkins University  has developed a leap week calendar called the Hanke Henry Calendar.  The HHPC uses months with lengths of 30:30:31 per quarter, i.e. 30-30-31–30-30-31–30-30-31–30-30-31, +7 in a leap year. Alas, like Dr. Bromberg in his Symmetry Calendars, Henry uses the names of the current months of the Gregorian Calendar for the names of the months in the HHPC. This can cause some confusion when trying to determine to which calendar the given date refers.

Also, there is a proposal to use the format of the World Calendar with Leap Weeks. The World Calendar uses months with lengths of 31:30:30 per quarter, i.e. 31-30-30-31-30-30-31-30-30-31-30-30.

To help alleviate this confusion, and to facilitate the use of either calendar simultaneously with the current Gregorian Calendar, Walter Ziobro likewise proposed the use of unique alternate month names for use with the Hanke Henry Calendar, and with the World Calendar with Leap Weeks. The base of each name is derived from the corresponding Gregorian month name.

Henry has proposed a leap year rule in which the leap week is added to any year that begins or ends on Thursday in the Gregorian Calendar.  This is virtually the same as the rule for the 53rd, or leap week, in the ISO 8601 week dating system, the only difference is that Henry started each year on a Sunday, instead of a Monday.  

The proposal for the WCLW uses a 62-year leap week cycle.  Ziobro would replace that rule with the ISO 8601 leap week rule to make it compatible with other proposals using the same rule. He uniformly adds the leap week to the end of the last month.    

Sunday start[]

30:30:31 and 31:30:30 leap-week calendars starting Sundays
MM QM Hanke-Henry Permanent Calendar (HHPC-Sun) World Calendar with Leap Weeks (WCLW)
Name Abbr Days Start Name Abbr Days Start
01 Q11 Janus (Jas) 30 W52-7* Janus (Jas) 31 W52-7*
02 Q12 Februs (Fbs) 30 W05-2 Febum (Fbm) 30 W05-3 
03 Q13 Marcus (Mrs) 31 W09-4 Marchum (Mrm) 30 W09-5
04 Q21 Aprilus (Aps) 30 W13-7 Aprilus (Aps) 31 W13-7 
05 Q22 Mayus (Mys) 30 W18-2 Mayum (Mym) 30 W18-3 
06 Q23 Junus (Jns) 31 W22-4 Junum (Jnm) 30 W22-5
07 Q31 Julus (Jls) 30 W26-7 Julus (Jls) 31 W26-7 
08 Q32 Augustus (Aus) 30 W31-2 Augustum (Aum) 30 W31-3 
09 Q33 Septus (Sps) 31 W35-4 Septum (Spm) 30 W35-5
10 Q41 Octus (Ocs) 30  W39-7 Octus (Ocs) 31 W39-7 
11 Q42 Novus (Nvs) 30  W44-2 Novum (Nvm) 30 W44-3 
12 Q43 Decus (Dcs) 31/38 W48-4 Decum (Dcm) 30/37 W48-5 

*W53-7 in year after leap week.

Although they are of different length, the first month of each quarter starts on the same date in both system and can therefore share the same name in both systems, because the 31st day of it is never ambiguous. Otherwise, the 30:30:31 month names always end in -us, while the 31:30:30 month names end in -um.

Monday start[]

Since the late 2010s, the Hanke-Henry website has been displaying a modified version of their calendar, which retains the 30-30-31 month-day quarter format, but which begins each quarter on a Monday. This revision can be used with the following alternate names from Alternative month names for use with Accounting Leap Week Calendars:

30:30:31 leap-week calendars starting Mondays
MM QM Hanke-Henry Permanent Calendar (HHPC-Mon)
Name Abbr Days Start
01 Q11 Janum (Jam) 30 W01-1
02 Q12 Februm (Fbm) 30 W05-3
03 Q13 Marchum (Mrm) 31 W09-5
04 Q21 Aprilum (Apm) 30 W14-1
05 Q22 Mayum (Mym) 30 W18-3
06 Q23 Junum (Jnm) 31 W22-5
07 Q31 Julum (Jim) 30 W27-1
08 Q32 Augustum (Aum) 30 W31-3
09 Q33 Septum (Spm) 31 W35-5
10 Q41 Octum (Ocm) 30 W40-1
11 Q42 Novum (Nvm) 30 W44-3
12 Q43 Decum (Dcm) 31/38 W48-5

However, this system reuses the names and abbreviations used for the 31:30:30 WCLW above, but is not compatible with it.