Dates before 1582 are interpreted in the proleptic Gregorian calendar.
Mayan priests divided the 584-day cycle of Venus into four phases. The beginning of each phase counted as dangerous. At the heliacal rising in particular, Venus was drawn as a god attacking with spears.
Twenty day names are paired with thirteen numbers. Every day is unique and comes round again only after 260 days. The origin of the number 260 is disputed. Researchers have linked it to the human gestation period, to the interval between solar zenith passages at the latitude of Tikal, and to a sacred 13 × 20 vigesimal-tridecimal scheme.
Your birth date fixes your own Tzolk'in day, and in the Mayan cosmovision that day was tied to personal destiny.
The Haab' consists of eighteen months of twenty days plus a five-day Wayeb' period. It comes close to the tropical year without matching it. Because no day is ever intercalated, it drifts by roughly 365 days over 1,500 years.
The Wayeb' period counted as dangerous. Portals were said to open in those days, so people fasted ritually and stayed at home.
The Calendar Round comes out of the combination of Tzolk'in and Haab'. A given date, "4 Ajaw 8 Kumk'u" for example, repeats only after exactly 52 years. In Mayan culture this was the measure of generational renewal.
At the close of the 52-year cycle the New Fire ceremony was performed. All fires were put out and then lit again.
The Long Count is a system that numbers days along a single line. It gives the days elapsed since the mythological beginning (4 Ajaw 8 Kumk'u, equivalent in the GMT correlation to 11 August 3114 BCE). Thirteen baktuns = 1,872,000 days ≈ 5,125 years, and that span makes one "Great Cycle."
The date 13.0.0.0.0, the end of the Great Cycle, fell on 21 December 2012. The popular "end-of-the-world" readings come from that date.
The correlation constant is the bridge between the Long Count day-number and the modern Julian Day Number. It makes Long Count 0.0.0.0.0 correspond to JDN 584283 (Gregorian 11 August 3114 BCE).
The alternative correlations GMT+1 (584284) and GMT+2 (584285) are still debated in the literature. This tool uses 584283, the constant most scholars accept.
The underworld has nine deities and each of them rules one night in turn. Classic-period inscriptions give the Lord of the Night alongside the Long Count date. The names and identities of these nine gods have not been deciphered. Only G9 is associated with the aged god Pauahtun.
The Tzolk'in (260), Haab' (365) and Lords of the Night (9) cycle recurs every 170,820 days, approximately every 468 years.
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The 20 Tzolk'in day signs, the 19 Haab' months and the Nine Lords of the Night, with their names and meanings. The tool above computes Long Count and Calendar Round equivalents.
Twenty signs paired with the numbers 1 to 13 make the 260-day round.
Eighteen months of twenty days, plus the five days of Wayeb'.
In this nine-day cycle each day falls to one underworld deity.
Tzolk'in and Haab' together form the 52-year Calendar Round. The Long Count counts independently of that cycle.
About the Mayan calendar
The Tzolk'in is the 260-day sacred calendar of the Maya, formed by the combination of twenty named days (Imix, Ik', Ak'b'al, K'an, Chikchan, and so on) with thirteen numerals (1 to 13). Because 20 and 13 are coprime, every combination of number and name is unique and the cycle returns to its starting point only after 260 days. The Tzolk'in served as the principal divinatory and ritual calendar across Mesoamerica, and its origins may lie in the period of human gestation, the agricultural cycle of maize, or the synodic period of Venus.
The Haab' is the 365-day vague year of the Maya, divided into eighteen named winals or "months" of twenty days each (Pop, Wo', Sip, and so on through Kumk'u), followed by a five-day terminal period called Wayeb'. Because no leap day is inserted, the Haab' drifts against the tropical year by roughly one day every four years, the same fixed-length structure as the Egyptian civil year. The Haab' was used for agricultural and civil purposes and provides the second half of the Calendar Round.
The Calendar Round is the combination of the 260-day Tzolk'in and the 365-day Haab', producing a cycle of 18,980 days, exactly 52 Haab' years or 73 Tzolk'in cycles, before any given pairing of Tzolk'in and Haab' dates returns. This 52-year period was the principal mid-range timekeeping unit across pre-Columbian Mesoamerica, marking the great cycles of personal and political life. The completion of a Calendar Round was attended by major rituals, among the Aztecs the famous Toxiuh Molpilia or "binding of the years".
The Long Count is a linear day-count, used principally on Classic Maya monuments, that records the number of days elapsed since a mythical zero point, the beginning of the present world era, in units of k'in (1 day), winal (20 days), tun (360 days), k'atun (7,200 days), and b'ak'tun (144,000 days). The Goodman-Martínez-Thompson (GMT) correlation, with its now-standard constant of 584,283, places this zero point on 11 August 3114 BCE in the proleptic Gregorian calendar; the celebrated "end" of the thirteenth b'ak'tun fell on 21 December 2012. Epigraphic and archaeoastronomical work by Martin and Skidmore (2012), based on the Poco Uinic eclipse record, proposes a 584286 variant, and high-precision radiocarbon dating (Kennett et al. 2013) independently supports the GMT family; 584283 remains the standard constant.
The Venus table in the Dresden Codex (pages 24 and 46-50) is a sophisticated Late Postclassic Maya astronomical document that tracks the synodic period of Venus, traditionally taken as 584 days, across a great cycle of sixty-five Venus periods (37,960 days = 104 Haab' years). It records the four phases of Venus, namely morning star, superior conjunction, evening star and inferior conjunction, and identifies particular dates as ominous for warfare, when Venus first appears as morning star (heliacal rising). The table is one of the most accurate pre-telescopic Venus computations known, with corrections built in to maintain alignment over centuries.
The Nine Lords of the Night (Bolontiku) are a cycle of nine deities, identified epigraphically as G1 through G9, that rule successive nights and form an additional layer of ritual significance attached to each date in the Long Count. The Wayeb' is the five-day terminal period of the Haab' year, considered an inauspicious and dangerous time of liminality between years; it was marked by abstention from many normal activities and by purification rituals. Together, the Lords of the Night and the Wayeb' show how richly stratified Maya time was, with multiple overlapping cycles of meaning attached to every date.