The Shift Calendar is not a calendar (proposal) by itself, but a supplementary concept that is compatible with any calendar that has 91-day, i.e. 13-week quarters arranged in 3 months of 30 days twice and 31 days once or 3 months of 30 days and 1 extra day outside the month cycle. It works well with leap-week calendars, but probably better with leap-day calendars. The idea is to define several shift plans and work week independent of the actual 7-day week, but fixed to the calendar, cf. market weeks and Indonesian pawukon.

There are 5 cycles of 6 days called hexads and, likewise, 6 cycles of 5 days, pentads, per month. In months 31 days long, the final day is a holiday. Leap days and weeks and intercalary days are treated like holidays. Every hexad can also be subdivided into 2 sub-cycles of 3 days each, i.e. triads. Each cycle, whether 3, 5 or 6 days long, has one free day, which alternates among shift groups. There are also 3 larger cycles of 10 days per month, named decads, where each includes 3 days off. A half month of 3 pentads or 5 triads is called a crescent.

An integer number of cycles with 9 days, termed nonads, or 18 days fit well into the 90 regular days of a quarter, but they do not align with the cycles mentioned above inside 30-day months.

Normal 7-day weeks and 13-day cycles are the only ones which complete the 91 days of a quarter without holiday.

Quarter layout (with holiday at the end)
Triad 3 T01 T02 T03 T04 T05 T06 T07 T08 T09 T10 T11 T12 T13 T14 T15 T16 T17 T18 T19 T20 T21 T22 T23 T24 T25 T26 T27 T28 T29 T30 H
1T0 1T1 1T2 1T3 1T4 1T5 1T6 1T7 1T8 1T9 2T0 2T1 2T2 2T3 2T4 2T5 2T6 2T7 2T8 2T9 3T0 3T1 3T2 3T3 3T4 3T5 3T6 3T7 3T8 3T9 H
Pentad 5 P01 P02 P03 P04 P05 P06 P07 P08 P09 P10 P11 P12 P13 P14 P15 P16 P17 P18 H
1P1 1P2 1P3 1P4 1P5 1P6 2P1 2P2 2P3 2P4 2P5 2P6 3P1 3P2 3P3 3P4 3P5 3P6 H
Hexad 6 H01 H02 H03 H04 H05 H06 H07 H08 H09 H10 H11 H12 H13 H14 H15 H
1H1 1H2 1H3 1H4 1H5 2H1 2H2 2H3 2H4 2H5 3H1 3H2 3H3 3H4 3H5 H
Decad 10 D1 D2 D3 D4 D5 D6 D7 D8 D9 H
1D1 1D2 1D3 2D1 2D2 2D3 3D1 3D2 3D3 H
Crescent 15 C1 C2 C3 C4 C5 C6 H
1C1 1C2 2C1 2C2 3C1 3C2 H
Month 30 M1 M2 M3 H
Nonad 9 N0 N1 N2 N3 N4 N5 N6 N7 N8 N9 H
18 E1 E2 E3 E4 E5 H
Week 7 W01 W02 W03 W04 W05 W06 W07 W08 W09 W10 W11 W12 W13
13 S1 S2 S3 S4 S5 S6 S7
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