The 260-day sacred calendar
Two independent gears — the numbers 1–13 and a fixed ring of 20 named days — turn together. A given number returns to a given day only after 260 steps (13 and 20 share no common factor). This count is attested across Mesoamerica for well over two millennia and is still kept today by K'iche', Ixil, Mam, Q'anjob'al and other daykeepers.
Origin theories
No source states why the count is 260 days. Several explanations are argued; they are not mutually exclusive, and none is proven.
- Human gestation. ~260 days approximates the interval from a missed first menses to birth; midwife-daykeepers in living tradition make this link explicitly.
- Zenith passage. Near 14–15° N (the latitude of Copán and much of the southern lowlands) the interval between the sun's two annual zenith transits is close to 260 days on one side of the year.
- Agricultural cycle. 260 days is roughly the maize planting-to-harvest span in parts of the highlands.
- Ritual arithmetic. 13 (levels of the upper world / a sacred number) times 20 (a full count, and the number of fingers and toes — the vigesimal base).
- Venus and eclipses. 260 divides evenly into longer astronomical periods used in the codical tables (e.g. 2 × 260 = 520 ≈ 3 eclipse half-years).
Antiquity
The earliest securely dated 260-count references come from Oaxaca (Monte Albán, San José Mogote Monument 3, ~600 BCE) — that is, from Zapotec rather than Maya contexts. The system was pan-Mesoamerican; the Maya inherited and elaborated it rather than inventing it.
The 20 trecenas
The 260-day round divides into twenty 13-day periods (trecenas, from Spanish trece). Each begins on number 1 and is named for its opening day sign. The current trecena is highlighted.
260 days at a glance
Each row is one of the 20 trecenas; each column is the number 1–13. Bold cells in the first column open a trecena. Tap any day to see when it next falls in the Gregorian year.
Tzolk'in for any date
The twenty day signs
Each entry is layered by evidentiary status. Toggle the filters to control which categories of claim are shown — Modern interpretations are hidden by default, per this reference's editorial policy. The current day sign is outlined.