The Aztec Calendar was basically similar to that of the Maya. The ritual day cycle was called Tonalpohualli and was formed, as was the Mayan Tzolkin, by the concurrence of a cycle of numerals 1 through 13 with a cycle of 20 day names, many of them similar to the day names of the Maya.



Where the Aztec differed most significantly from the Maya was in their more primitive number system and in their less precise way of recording dates. 

Normally, they noted only the day on which an event occurred and the name of the current year. This is ambiguous, since the same day, as designated in the way mentioned above, can occur twice in a year. Moreover, years of the same name recur at 52-year intervals, and Spanish colonial annals often disagree as to the length of time between two events. 

Other discrepancies in the records are only partially explained by the fact that different towns started their year with different months. The most widely accepted correlation of the calendar of Tenochtitlán with the Christian Julian calendar is based on the entrance of Cortés into that city on November 8, 1519, and on the surrender of Cuauhtémoc on August 13, 1521. According to this correlation, the first date was a day 8 Wind, the ninth day of the month Quecholli, in a year 1 Reed, the 13th year of a cycle. 

The Mexicans, as all other Meso-Americans, believed in the periodic destruction and re-creation of the world. The "Calendar Stone" in the Museo Nacional de Antropología (National Museum of Anthropology) in Mexico City depicts in its central panel the date 4 Ollin (movement), on which they anticipated that their current world would be destroyed by earthquake, and within it the dates of previous holocausts: 4 Tiger, 4 Wind, 4 Rain, and 4 Water.