Meza
What it is
The count kept by the Mexicayotl and dance communities, published by Arturo Meza Gutiérrez in «Arte de calcular el Cauhpohualli». It is the one that places the new year on 12 March, which is the date the community keeps.
Why it does not fit the others' formula
It is the only one of the five that is not an anchor correlation. Its tonalpohualli does not roll on without stopping: the numeral of the day depends on the numeral of the year, so it cannot be solved by subtracting an anchor at all. That is why the book carries thirteen tables and not one, and why the universal formula every calculator on the internet uses, (jdn − anchor) mod 260, simply does not fit it.
How it is computed
Five steps: find the Mexica year on the wheel of year bearers, with 1519 = 1 Ácatl; count the days elapsed since 12 March; take the sign from that count; open the year with ((n−1)×9) mod 13 + 1 and advance one per day and seven per veintena; and place the five nemontemi after the eighteen veintenas.
Worth knowing
The Mexica year is 365 days, and from 12 March to 12 March there are 366 in a Gregorian leap year. The book does not say where that day goes. The engine declares it a sixth nemontemi and continues the count one step, marked as derived rather than attested.
The algorithm
The full algorithm for this count lives as a file of its own, kept outside the code and sealed, so that it outlives the app and so that whoever inherits it knows what to implement.
What is published here is its data sheet — the anchor, the offset, when the day starts and when the year opens — and its control dates, which is what lets anyone check whether a calculation is right.
How to cite this page
Alma Mexica, «Meza», The five counts. Last revised 2026-09-17. https://almamexica.org/en/counts/meza/
Questions that reach this page
What is the Meza correlation?
One of the five correlations this site publishes for turning Gregorian dates into Aztec calendar dates. It is the one much of the Mexica dance community follows, and it differs from the others in how it divides the day: not into twenty-four equal hours but into eighty quarters of eighteen minutes, each with its own sign.
Why do Aztec calendar converters disagree?
Because each one fixes a different anchor: a specific Gregorian date matched to a specific Aztec day. From there the arithmetic is identical, so the gap between any two is always a fixed number of days. For the same date they may give 6-Tochtli or 2-Cozcacuauhtli, and there is no scholarly consensus on which is right.