Chac is a complete, accurate Maya calendar application.

Chac can find Maya calendar dates based on today’s date, any date, a Long Count, Tzolk’in, Haab’, Calendar Round, Julian day number, distance number, long reckoning , seatings in the cycle of God K and convert between the Julian and Gregorian calendars.

Chac is also an archaeoastronomy program. It can find the next heliacal or cosmical rising or setting of Venus and the visibility of the current inscription or date. Chac can find the next or last day with a lunar or solar eclipse and will give the time as 24 hour time in time zone -6 and the Julian date of maximum eclipse. Chac can find the the dates of solstices and equinoxes. Chac can find the zenith passage days for a site in the tropics.

Chac calculates the day of the week, Gregorian or Julian date, Julian day number, the Year Bearer, cycle of God K, Long Count, Tzolk’in, Haab’, nine Lords of the Night, lunar deity, moon age and lunation length. Chac can find the heliacal or cosmical risings or settings of Venus. Chac can find solar or lunar eclipses. Chac can find the Solstices and Equinoxes. Chac can find the Zenith passage dates for any site.

You can use a large range of correlation constants, any one of the six possible moon numbers, astronomical or historical dating, any of the four Year Bearer systems and appearance of the new moon or the disappearance of the waning moon. Chac can display a Long Count with head or symbolic glyphs.

Chac draws the results as a complete Maya calendar inscription.

An inscription with its preferences can be saved in Chac’s file format or it can be saved as graphics in tiff, pdf, jpg, png, jp2 or bmp formats. An inscription can also be copied to the clipboard where it will be posted as pdf and tiff. And as inscription data that can be pasted in another inscription window.

What’s New

Version 2.7.13

I fixed a bug in the eclipse panel that could cause it to miss the next eclipse on the day before.

I made various minor changes.

Ratings and Reviews

4.0 out of 5
1 Rating

1 Rating

Mike Beer ,


Certainly a useful program for people interested in and working with mesoamerican calendars. Date calculations done by hand are tedious at best, and prone to error. Having a programatic method is a great time saver.
It offers a large number of options for different correlation constants that are probably only of interest to those deeply involved in mesoamerican calendrics or who interpret things written by other authors.
The help files are interesting as a introduction to the topic and contain a set of refernces that are helpful for further study in the topic.
WIth the current media interest in "maya calendars" and the end of the bak'tun it is good to see an honest effort in a sensationalized topic.


Warren Anderson
5.8 MB

OS X 10.10.0 or later, 64-bit processor



Age Rating
Rated 4+
© 1999 - 2018 Warren Anderson all rights reserved


  • Family Sharing

    With Family Sharing set up, up to six family members can use this app.