The Aztec Calendar

The Aztec calendar was a complex calendar comprised of two separate systems that together created a 52 year cycle. Each system served an important purpose for the Aztecs in their daily and religious lives. Not only did they serve as a means to determine the passage of time, but both calendars provided guidance for the timing of religious ceremonies, festivals, and agriculture.

Aztec Calendar Structure

Two independent calendar systems comprised the 52 year cycle that is often known as the Calendar Round. At the end of each Calendar Round, the 52 year cycle began anew.

  1. The first of these calendar systems, the tōnalpōhualli, consisted of a 260 day cycle. This calendar was used as a guide for religious and divine purposes.
  2. The second calendar was called xiuhpōhualli and functioned as a year count with 365 days divided into months.

Xiuhpōhualli - The Year Count

The xiuhpōhualli, or the year count, was structured around solar cycles and was considered an agricultural calendar. However, time keeping was not its only purpose. The year count calendar dictated when festivals and ceremonies should be held. The 365 days were broken into two groups - 360 named days and 5 unnamed days. Each of the 360 named days were further divided into 18 periods of 20 days each.

Years were named based on the names Rabbit, Reed, Flint Knife, and House. They were then given sequential numbers up to 13, ensuring that once each name and number had been used a full calendar round of 52 years had been completed.

The 5 remaining unnamed days at the end of each year were considered unlucky. These days were added in an attempt for solar accuracy.

Tōnalpōhualli - The Day Count

Tōnalpōhualli, sometimes called the day count calendar, was considered one of the most important parts of the Aztec calendar system. This calendar was used to determine what god the day belonged to. Aztecs considered this important in order to retain balance between the multiple gods.

Each of the 260 days in this calendar were broken into 20 day periods in which each day had its own name, deity, and symbol. Every 13 days, an Aztec week would pass. At this point, the number of the day would revert to 1 while the name, deity, and symbol would continue to 20.

The day count calendar was not based on either solar or lunar patterns. Instead, it has been hypothesized that these numbers were chosen as they closely align to the human gestation period. Regardless of how these numbers were chosen, the day count calendar and year count calendar aligned roughly every 52 years.

Aztec Calendar Count Cycle

© Dick Thompson - Aztec Calendar Count Cycle


On the day count calendar, tonalpohualli, each day was given a day sign that correlated to a god. In addition, the number preceding the day sign was also related to a spirit or force that could determine the nature of a day. These two pieces of information helped determine what rituals should be performed that day.

In order, the 20 day signs and god associated with them were:

  1. Crocodile - Tonacatecuhtli, god of fertility and new beginnings
  2. Wind - Quetzalcoatl, god of intelligence
  3. House - Tepeyollotl, god of night and echoes
  4. Lizard - Huehuecoyotl, god of tricks and stories
  5. Snake - Chalchiuhtlicue, goddess of birth and water
  6. Death - Tecciztecatl, god of the moon
  7. Deer - Tlaloc, god of rain and thunderstorms
  8. Rabbit - Mayahuel, goddess of fertility
  9. Water - Xiuhtecuhtli, god of fire
  10. Dog - Mictlantecuhtli, god of death
  11. Monkey - Xochipili, god of flowers and creativity
  12. Grass - Patecatl, god of healing
  13. Reed - Tezcatlipoca, god of time and memory
  14. Jaguar - Tlazolteotl, goddess of the earth
  15. Eagle - Xipe Totec, god of rebirth and spring time
  16. Vulture - Itzpapalotl, goddess of purification and sacrifice
  17. Movement - Xolotl, god of sickness
  18. Stone Knife - Chalchihuihtotolin, god of sorcery
  19. Rain - Tonatiuh, god of the sun
  20. Flower - Xochiquetzal, goddess of flowers and love
Aztec Calendar Codex

© Paul K - Aztec Calendar Symbol Depictions

Aztec Festivals and Ceremonies

Within both the day and year calendar there were many Aztec celebrations. Several of these involved human sacrifice, although others required only animal or a blood sacrifice. Once a month in the year calendar a festival occurred. These occurred on the first day of that particular period.

Ceremonies and festivals occurred for many reasons but often were associated with planting, harvest, hunting, and fertility. Of particular focus for many festivals was agriculture. Priests organized all ritual and ceremony, while the remainder of the Aztecs participated in feasts and festivities.

In Spring, festivities occurred to honor Xipe Totec to invoke fertility and rebirth. The rituals associated with this included human sacrifice and lasted for 20 days. During the 20 day festival, captured warriors were sacrificed and flayed. Military ceremonies also typically took place during this festival.

An important festival took place at the end of each 52 year calendar round when the 2 calendars aligned. During this festival called New Fire Rites all fires were doused and the city was drenched in darkness. A man was then sacrificed and a fire was stared in his chest. From this fire, all fires in both homes and temples were relit.

At the end of the 360 named days, no festivities would occur for the 5 unnamed days at the end of the year. This unlucky period of time consisted of fasting and waiting for the year cycle to begin anew.

Aztec Calendar Stone

The Aztec Calendar Stone, sometimes called the Sun Stone, is an iconic Aztec stone sculpture. In the center of the stone is the face of the sun deity, Tonatiuh. On either side of the face, 2 claw like hands clutch human hearts. Intricate carvings and symbols surround the face in increasingly larger circles.

From the center, the first circle represents the four previous eras before the creation of the Sun Stone. The second circle represents the 260 day count. The third circle contains five points, likely relating to cardinal points. In the fourth and final ring there are 2 serpents and a carving thought to be the date the stone was created.

The specific purpose of the Calendar Stone is unknown, however, it is thought to be of religious or ceremonial uses.

Aztec Sun Stone at the National Museum of Anthropology of Mexico City

© Artotem - Aztec Calendar (Sun) Stone at the National Museum of Anthropology of Mexico City

Facts about the Aztec Calendar

  • There were 2 separate but connected calendars that together are referred to as the Aztec Calendar.
  • Every 52 years, the 2 calendars would align and the "Calendar Round" would begin again.
  • The 2 calendars were a year count with 365 days and a day count with 260 days.
  • The calendar served an important part in Aztec life and religion.
  • The 260 day count calendar was used for ritual.
  • In the day count calendar each day was assigned a different god, symbol, and number.
  • In the year count calendar, a festival was held in the beginning of every month.
  • At the end of every year there were 5 unnamed days that were considered unlucky.
  • When a calendar round had been completed, a festival involving human sacrifice called the New Fire Rites would occur to show the year had started fresh.
  • The Calendar Stone was thought to be used for religious purposes.