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The Octalendar is a perpetual leap week calendar design that divides the year into 8 months, called a spoke, of exactly 6 or 7 weeks, alternating 7:6. That means, every odd spoke has 49 days and every even spoke has 42 days, except for the last, eighth one in leap years when it has 49 days instead.

The date format is ISO-like ±YYYY-S-W-D. All usual date conventions comply with ISO 8601, i.e. weeks start on Monday and the leap week depends on the Gregorian leap rule and year count. Among other things this means, the year number, CCYY or YYYY, is always the same as in ISO week date and the day of the week, D, is the same in Octalendar and Gregorian. Today is 2024-5-2-4 in Octalendar and 2024-07-11 = 2024-W28-4 by ISO 8601. If more disambiguation from Gregorian dates is required, the lowercase letter o can be added after the year; hyphens become optional then: 2024o524.

Two adjacent spokes can be grouped to form a quarter or season of 13 weeks. Only the final quarter spans 14 weeks once per 5 to 6 years.

The name spoke for its months is inspired by the Celtic Wheel of the Year which also divides the year into eight parts, but at annual astronomic events. Lacking any better source, their names are also derived from the Celtic festival seasons.

Cal7 also has months with 7 weeks, but alternates them with ones of 8 weeks (8:7), totalling in just 7 months.

Relation to other leap week calendars
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 53
13mon Janon Febron Marchon Apron Mayon Junion Extron Julon Augon Septon Octon Novon Decon †
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 Febral Marchal Maydor Junidor Augaire Septaire Novose Decose †
Quarter quart 1 quart 2 quart 3 quart 4
7:6 Bol Sar Tan Lit Nas Mon Sam Yul †
4:5* Janose Febrose Marchose Aprilose Mayose Junal Julidor Augidor Septidor Octidor Novidor Decaire †
9:9:8 sester 1 sester 2 sester 3 sester 4 sester 5 sester 6
5:5:6:5 Primoth Secoth Tertoth Quaroth Quintoth Sixtoth Septoth Octoth Novoth Decoth †
10:11 quinter 1 quinter 2 quinter 3 quinter 4 quinter 5
8:7 Monmonth Tuesmonth Wednesmonth Thursmonth Frimonth Saturmonth Sunmonth †
 Terms Spring semester Summer break Fall semester
Winter semester Spring break Summer semester Fall break Winter semester
Epiphany/Hilary trimester Trinity trimester Summer break Michaelmas trimester
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