Aztec Calendar Calculator
The Aztecs kept two calendars at once: the sacred 260-day count of twenty day signs, and the 365-day solar year. Enter any date below to find its day sign and number in the tonalpohualli, its place in the solar year, and its Long Count, computed with the standard correlation and calibrated on verified historical dates.
Updated August 23, 2026: Goodman-Martinez-Thompson correlation, calibrated on August 13, 1521 (1 Coatl) and December 21, 2012 (13.0.0.0.0, 3 Kankin).
The Two Calendars
The Aztec calendar is not one count but two, running together like meshed wheels. The tonalpohualli is the sacred count: 260 days made of twenty day signs and thirteen numbers. Each day is both a sign and a number (1 Crocodile, 2 Wind, 3 House, and so on through the wheel), and the pair repeats every 260 days. This is the calendar of divination, of naming days, and of the character of birth: in the tradition, the day sign of your birth describes your nature and your path, the same way a zodiac sign does in the West.
The xiuhpohualli is the solar year: 365 days divided into eighteen months of twenty days, plus five unlucky days at the end (the Wayeb). The two wheels mesh: a given tonalpohualli day and a given xiuhpohualli day coincide only once every 18,980 days, exactly 52 solar years. That period is the Calendar Round, and its completion was the great ceremony of the Aztec year, the binding of the new fire.
The Twenty Day Signs
How the Calculation Works
The calculator converts your date to a Julian Day number, the continuous day count used by astronomers, then applies the Goodman-Martinez-Thompson correlation, the standard correlation of Mesoamerican calendars. The correlation is anchored to the creation date: August 13, 3114 BCE is the day 0.0.0.0.0 of the Long Count, the linear count of days written in five places (baktun, katun, tun, uinal, kin).
The calibration is verified against two independently documented dates. August 13, 1521, the fall of Tenochtitlan, is recorded as the day 1 Coatl in the tonalpohualli, and the calculator reproduces that exactly. December 21, 2012 is recorded as the end of the 13th baktun, 13.0.0.0.0, with the day 3 Kankin in the 365-day count, and the calculator reproduces both. Two independent anchors mean the whole range of dates is reliable.
How to Read Your Date
Your day sign is the character of the day you were born, and the number (1 through 13) is its intensity. In the tradition, a 1 carries the pure sign, a 13 the fullest expression before the cycle turns. The meaning of each sign is given in the table above: read your sign's character as the nature of the day, and your number as the strength of that nature. The 365-day count places your date in the solar year, and the Long Count places it in the absolute flow of days since the creation.
Frequently Asked Questions
What is the Aztec calendar?
The Aztec calendar is really two calendars running together. The tonalpohualli is the sacred 260-day count of 20 day signs and 13 numbers, used for divination and naming days. The xiuhpohualli is the 365-day solar year of 18 months of 20 days plus 5 unlucky days. The two wheels mesh every 52 years, the famous Calendar Round.
What is my Aztec day sign?
Your Aztec day sign is one of the 20 signs of the tonalpohualli that rules your birth date: Cipactli (Crocodile), Ehecatl (Wind), Calli (House), and so on. Each sign carries a character and a destiny in the tradition, the same way a zodiac sign does in Western astrology. Enter your date in the calculator to find yours.
How is the Aztec calendar date calculated?
The calculator converts your date to a Julian Day number and applies the Goodman-Martinez-Thompson correlation, the standard correlation used by archaeologists. The correlation is calibrated on known historical dates: August 13, 1521, the fall of Tenochtitlan, was 1 Coatl, and December 21, 2012 was 13.0.0.0.0, the end of the 13th baktun, with the day 3 Kankin in the 365-day count.
What is the Calendar Round?
The tonalpohualli (260 days) and the xiuhpohualli (365 days) are independent wheels. Because 260 and 365 share the least common multiple of 18,980 (52 solar years), any combination of a tonalpohualli day and a xiuhpohualli day repeats only once every 52 years. The completion of a Calendar Round was a great ceremony in Aztec tradition.
What is the Long Count?
The Long Count is the linear day count that runs beyond the 52-year rounds, written as five places: baktun, katun, tun, uinal, and kin (144,000, 7,200, 360, 20, and 1 days). It begins on August 13, 3114 BCE (the creation date, 0.0.0.0.0) and is the calendar that ended its 13th baktun on December 21, 2012.
Sources
The correlation used is the Goodman-Martinez-Thompson (GMT) correlation (Julian Day 584283 = 0.0.0.0.0), the standard of Mesoamerican scholarship. The day signs, month names, and calendar structure follow the classical sources of the Aztec tradition (the Codex Borbonicus and the colonial chronicles). The calibration anchors (August 13, 1521 = 1 Coatl; December 21, 2012 = 13.0.0.0.0, 3 Kankin) are the standard documented dates of the scholarship.