Businesses sometimes use leap week calendars for bookkeeping, but differ in the format used. These formats usually divide the year into equal quarters of 91 days each , but within those quarters often differ between using nearly equal months of 31-30-30 , 30-31-30 , or 30-30-31 days, or using whole weeks of 5-4-4 , 4-5-4 or 4-4-5 weeks.
Assuming an ISO weekday system is used, with ISO W53 being the same leap week in all cases, there are thus 6 possible formats. These formats can have the same start date for each quarter, but different month lengths for each of the 6 possible formats. These 6 possible formats can be given unique month names which thus allow all 6 of them to be used simultaneously and unambiguously. The following is an example of such a month naming scheme:
Systematic month names
Week
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
13mon
Janoon
Febroon
Marchoon
Aproon
Mayoon
Junioon
Extroon
Juloon
Augoon
Septoon
Octoon
Novoon
Decoon
5:4:4
Janaire
Febraire
Marchose
Aprilose
Mayose
Junal
Julial
Augial
Septidor
Octidor
Novidor
Decaire
4:5:4
Janose
Febrose
Aprial
Mayal
Julidor
Augidor
Octaire
Novaire
4:4:5
Febrose
Marchal
Mayal
Junidor
Augidor
Septaire
Novaire
Decose
31:30:30
Janum
Febra
Marcha
Aprilum
Maya
Juna
Julium
Auga
Septa
Octum
Nova
Deca
30:31:30
Janum
Februm
Aprilum
Mayum
Julium
Augum
Octum
Novum
30:30:31
Februm
Marchum
Mayum
Junum
Augum
Septum
Novum
Decum
Q
Quartose
Quartial
Quartidor
Quartaire
First month per quarter longer
Month
31-30-30
Days
Start
Month
5-4-4
Days
Start
Janum
(Jam)
31
W01-1
Janaire
(Jar)
35
W01-1
Febra
(Fba)
30
W05-4
Febraire
(Fbr)
28
W06-1
Marcha
(Mra)
30
W09-6
Marchose
(Mro)
28
W10-1
Aprilum
(Apm)
31
W14-1
Apriose
(Apo)
35
W14-1
Maya
(Mya)
30
W18-4
Mayose
(Myo)
28
W19-1
Juna
(Jna)
30
W22-6
Junal
(Jnl)
28
W23-1
Julium
(Jlm)
31
W27-1
Julial
(Jll)
35
W27-1
Auga
(Aua)
30
W31-4
Augial
(Aul)
28
W32-1
Septa
(Spa)
30
W35-6
Septidor
(Spd)
28
W36-1
Octum
(Ocm)
31
W40-1
Octidor
(Ocd)
35
W40-1
Nova
(Nva)
30
W44-4
Novidor
(Nvd)
28
W45-1
Deca
(Dca)
30/37
W48-6
Decaire
(Dcr)
28/35
W49-1
Middle month per quarter longer
Month
30-31-30
Days
Start
Month
4-5-4
Days
Start
Janum
(Jam)
30
W01-1
Janose
(Jao)
28
W01-1
Februm
(Fbm)
31
W05-3
Febrose
(Fbo)
35
W05-1
Marcha
(Mra)
30
W09-6
Marchose
(Mro)
28
W10-1
Aprilum
(Apm)
30
W14-1
Aprial
(Apl)
28
W14-1
Mayum
(Mym)
31
W18-3
Mayal
(Myl)
35
W18-1
Juna
(Jna)
30
W22-6
Junal
(Jnl)
28
W23-1
Julium
(Jlm)
30
W27-1
Julidor
(Jld)
28
W27-1
Augum
(Aum)
31
W31-3
Augidor
(Aud)
35
W31-1
Septa
(Spa)
30
W35-6
Septidor
(Spd)
28
W36-1
Octum
(Ocm)
30
W40-1
Octaire
(Ocr)
28
W40-1
Novum
(Nvm)
31
W44-3
Novaire
(Nvr)
35
W44-1
Deca
(Dca)
30/37
W48-6
Decaire
(Dcr)
28/35
W49-1
Last month per quarter longer
Month
30-30-31
Days
Start
Month name
4-4-5
Days
Start
Janum
(Jam)
30
W01-1
Janose
(Jao)
28
W01-1
Februm
(Fbm)
30
W05-3
Febrose
Febral
(Fbo)
28
W05-1
Marchum
(Mrm)
31
W09-5
Marchal
(Mrl)
35
W09-1
Aprilum
(Apm)
30
W14-1
Aprial
(Apl)
28
W14-1
Mayum
(Mym)
30
W18-3
Mayal
Mayidor
(Myl)
28
W18-1
Junum
(Jnm)
31
W22-5
Junidor
(Jnd)
35
W22-1
Julium
(Jlm)
30
W27-1
Julidor
(Jld)
28
W27-1
Augum
(Aum)
30
W31-3
Augidor
Augaire
(Aud)
28
W31-1
Septum
(Spm)
31
W35-5
Septaire
(Spr)
35
W35-1
Octum
(Ocm)
30
W40-1
Octaire
(Ocr)
28
W40-1
Novum
(Nvm)
30
W44-3
Novaire
Novose
(Nvr)
28
W44-1
Decum
(Dcm)
31/38
W48-5
Decose
(Dcr)
35/42
W48-1