Julian Date Converter
Mesoamerican cycle conversion
Aztec Date Converter
Convert Gregorian dates into an arithmetic Aztec Tonalpohualli and Xiuhpohualli model, or convert a full cycle tuple back to Gregorian.
Live output
Result
Choose a direction, enter a Gregorian date or full Aztec cycle tuple, and the model result appears here.
Guide
Aztec Date Converter for cycle tuples
This Aztec Date Converter changes Gregorian dates into an arithmetic Tonalpohualli and Xiuhpohualli model, then converts a complete model tuple back into a Gregorian date. It is intended for working with the cycle fields produced by this page, not for resolving every historical Aztec correlation debate.
The reverse input includes a cycle round, the 260-day ritual number and sign, the 365-day solar month and day, and the year bearer. Those fields are needed because repeating Mesoamerican cycles do not identify a unique Gregorian day without an explicit model anchor.
What this converter handles
Tonalpohualli and Xiuhpohualli fields from one day count
The converter first maps a Gregorian date to a Julian Day Number, then applies the page's arithmetic anchor constants to derive the ritual-day and solar-year positions. The same model is used in reverse by searching the 18,980-day Calendar Round segment for a matching tuple.
Because the implementation is a transparent arithmetic model, it can be useful for repeatable calculations and examples. It should not be treated as a documentary reconstruction of every local or colonial-era Aztec calendar source.
Gregorian to Aztec cycle fields
Enter a Gregorian date and return the Tonalpohualli number/sign, Xiuhpohualli month/day, year bearer, and model round.
Aztec tuple to Gregorian
Enter the full round:number-sign-day-month-yearbearer tuple and convert it back through the same anchor model.
Calendar Round context
The model makes the repeated 260-day and 365-day cycles explicit instead of hiding the correlation assumption.
How to use it
Use the exact tuple format shown in the form
Choose Gregorian to Aztec when your source date is Gregorian. Choose Aztec to Gregorian when your source is a full tuple from this arithmetic model.
Reverse input accepts an optional round prefix, followed by number, sign, solar day, solar month, and year bearer. If the round prefix is omitted, the converter treats the input as round 0.
Convert from Gregorian
Enter a date such as 2026-06-30 to get the matching model tuple and reference JDN.
Convert from an Aztec tuple
Use input such as 0:1-Cipactli-01-Atlacahualo-Acatl, preserving the hyphen-separated fields.
Check invalid cycle values
The converter rejects number values outside 1-13, unknown signs or months, and impossible Nemontemi day values.
Reference examples
Reference conversions from the local implementation
These examples come from the local converter functions. They demonstrate the exact tuple syntax required for reverse conversion and the JDN bridge used internally.
Gregorian to Aztec
The Gregorian date 2026-06-30 converts to tuple 0:1-Cipactli-01-Atlacahualo-Acatl with reference JDN 2461222.
Aztec to Gregorian
The tuple 0:1-Cipactli-01-Atlacahualo-Acatl converts back to Gregorian 2026-06-30 in this arithmetic model.
FAQ
Aztec conversion questions
Aztec calendar searches often mix cycle names, year bearers, and historical correlation questions. These answers keep the page tied to the model implemented by the converter.
Is one Tonalpohualli day enough for reverse conversion?
No. The 260-day cycle repeats. Reverse conversion requires the full tuple, including the model round and Xiuhpohualli fields.
Does this reconstruct historical Aztec dates from documents?
No. It is an arithmetic conversion model. Documentary dates may need specialist handling of regional practice, colonial transcription, and correlation choices.
Why does the input include a round prefix?
The 260-day and 365-day cycles realign every 18,980 days. The round prefix tells the converter which repeated Calendar Round segment to use.
Reference
Calendar implementation reference
The converter uses absolute-day arithmetic and clearly labeled cycle assumptions, the same general approach used by calendrical calculation references for historical calendar models.