Structure: 18 winals plus Wayeb'
The Haab' is built from winals, 20-day months. Eighteen winals give 360 days; the final five days, Wayeb', complete the 365. There is no leap correction, so the Haab' drifts roughly a quarter-day per year against the tropical year — academics call it a vague year. Days inside a winal are numbered 0–19 in Classic inscriptions (the 0 day represents the seating of that month). Most algorithms use 0–19; some popular calendars shift to 1–20 — pick a convention and stick with it.
The 19 Haab' months
The 18 named winals run: Pop, Wo', Sip, Sotz', Sek, Xul, Yaxk'in, Mol, Ch'en, Yax, Sak, Keh, Mak, K'ank'in, Muwan, Pax, K'ayab, Kumk'u, followed by Wayeb'. Pop opens the year — 0 Pop is the Maya New Year. Each month has glyphic associations with seasons, deities, and farming tasks. Yucatec spellings shown above are the academic standard; older sources use Spanish-derived spellings (Uo, Zip, Zotz, Cumku, Uayeb) you will see across the web.
Wayeb': the five nameless days
The Wayeb' (or Uayeb) closes the Haab' year. Considered ominous and liminal — a no-time between years — these days were treated with caution. People avoided travel, public business, even bathing. The transition from Wayeb' to 0 Pop was the Maya New Year, marked by ceremonies that installed a new Year Bearer. Modern day-keepers still observe Wayeb' as a period for retreat and reflection.
Why the Haab' matters in astrology
The Haab' itself is not a personality calendar — it is a civic timekeeper. But two roles tie it to astrology. First, the Year Bearer (Mam) is the Tzolk'in sign that lands on 0 Pop; only four signs can ever serve, rotating each year. Second, the Haab'-Tzolk'in pair forms the Calendar Round, an 18,980-day (52-year) cycle in which any specific date like 4 Ajaw 8 Kumk'u recurs only once per lifetime.
Haab' and the Tzolk'in: how they mesh
A complete Maya date pairs Haab' and Tzolk'in: e.g. 1 Ix 0 Pop. The Tzolk'in advances by one each day; so does the Haab'. Their lowest common multiple (LCM 260, 365) is 18,980 days — a Calendar Round of about 52 solar years. Pre-Long-Count Mesoamerican cultures used this pair alone for chronology, sufficient inside a human lifetime.