About the Calendar Correlation

This plugin uses the Alfonso Caso – Nicholson correlation, the most widely accepted scholarly standard for converting Gregorian dates to the Aztec calendar. This correlation is anchored to the historically documented date of August 13, 1521 (the fall of Tenochtitlan), which corresponds to the day 1-Cóatl (Serpent) in the Aztec tonalpohualli.

It’s important to note that multiple valid correlations exist in Aztec calendar studies. Scholars like Alfonso Caso, H.B. Nicholson, Zelia Nuttall, and Rubén Ochoa have proposed different correlations based on various colonial sources and astronomical observations. We chose the Caso-Nicholson correlation because it is the most widely used by academic institutions, aligns with other Mesoamerican calendars (including the Mayan calendar), and is supported by multiple independent historical sources documenting the same correlation date. This correlation is used by major universities and research institutions studying Mesoamerican history, making it the de facto standard for contemporary Aztec calendar calculations.

While other correlations may differ by a few days, the Caso-Nicholson correlation provides the most broadly accepted framework for understanding your birth date’s significance in the ancient Aztec tradition.