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:

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 (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 (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 (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 (Nvr) 28 W44-1
Decum (Dcm) 31/38 W48-5 Decose (Dcr) 35/42 W48-1
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