How this instrument works
The Maya calendar system is really three interlocking counts running simultaneously, not one. The Long Count is a linear day count from a fixed mythical creation date, written as five numbers separated by dots (baktun.katun.tun.winal.kin), each place representing a different span of days, similar in spirit to how a year.month.day date breaks a day count into readable units. The Tzolk'in is a 260-day sacred cycle formed by combining a number from 1 to 13 with one of 20 named days, repeating every 260 days. The Haab' is a roughly solar 365-day cycle of eighteen 20-day named months plus a short 5-day period called Wayeb', repeating every 365 days.
Converting between the Maya count and our Gregorian calendar requires a 'correlation constant' — a fixed offset pinning one specific Maya date to one specific Gregorian date, since the Long Count's zero point predates any calendar record that survives to confirm it directly. This instrument uses the GMT (Goodman-Martinez-Thompson) correlation, the constant accepted by the great majority of Mayanist scholars and virtually all popular tools, anchored to the well-documented modern reference point of December 21, 2012 corresponding to Long Count 13.0.0.0.0 — the widely reported 'end of the 13th baktun' date.
Under the GMT correlation, the Long Count's creation date, 0.0.0.0.0, falls on August 11, 3114 BCE in the proleptic Gregorian calendar (a Gregorian calendar extended backward before its actual 1582 adoption, used here purely as a common reference point for dates that predate it). Dates before that creation point have no defined Long Count under this system and aren't supported here.
A handful of alternative correlation constants exist in the academic literature, differing from GMT by anywhere from a day to several days, and using one of those instead would shift every result here by that same fixed offset. GMT remains the standard choice in essentially all popular and most academic contexts today, which is why it's the one used throughout this instrument.
- Enter Gregorian date — it defaults to today's date, or pick any other date you want converted.
- Read Long Count for the baktun.katun.tun.winal.kin linear day count from the Maya creation date.
- Read Tzolk'in for the 260-day sacred-cycle date — a number from 1 to 13 paired with one of 20 day names.
- Read Haab' for the 365-day solar-cycle date — a day number paired with one of 18 month names, or Wayeb'.
- Try December 21, 2012 to reproduce the famous 'end of the 13th baktun' Long Count exactly.
Worked example — December 21, 2012
December 21, 2012 is the single most famous modern Long Count reference date — the day the count rolled from 12.19.19.17.19 to 13.0.0.0.0, popularly (and incorrectly) reported as an 'end date' for the Maya calendar. Entering that date, Long Count reads 13.0.0.0.0 exactly, marking the completion of the 13th baktun since the creation date.
Tzolk'in reads 4 Ajaw, and Haab' reads 3 K'ank'in. Both of these are independently documented, uncontested facts about this specific historical date, and this instrument's own creation-date derivation reproduces them exactly — a strong internal check that the correlation constant and day-count arithmetic underlying it are working correctly, since 13.0.0.0.0 also happens to share its Tzolk'in name, 4 Ajaw, with the creation date itself (0.0.0.0.0), a consequence of 13 baktuns dividing evenly into whole 260-day Tzolk'in cycles.
Questions
What is the Maya Long Count calendar?
It's a linear day count running continuously from a fixed mythical creation date, written as five numbers separated by dots — baktun.katun.tun.winal.kin — where each position represents a progressively larger span of days (1 kin = 1 day, 1 winal = 20 days, 1 tun = 360 days, 1 katun = 7,200 days, 1 baktun = 144,000 days). Unlike the Tzolk'in and Haab' cycles, which repeat, the Long Count simply keeps counting upward indefinitely, functioning much like a running day-number odometer since the Maya creation date.
What does a Long Count date like "13.0.0.0.0" actually mean?
Reading left to right, it means 13 baktuns, 0 katuns, 0 tuns, 0 winals, and 0 kins have elapsed since the creation date — in other words, exactly 13 x 144,000 = 1,872,000 days have passed. December 21, 2012 is the Gregorian date that corresponds to that exact day count under the GMT correlation, which is why it marks the completion of the 13th baktun.
What is the Tzolk'in and how is it built?
The Tzolk'in is a 260-day sacred/ritual cycle, formed by pairing a number from 1 to 13 with one of 20 named days (like Ajaw, Ik', or Kimi), cycling through both simultaneously. Since 13 and 20 share no common factor, every combination of number and day name recurs only once every 260 days (13 x 20), giving the cycle its full length before any specific number-and-name pairing repeats.
What correlation constant does this converter use, and why does it matter?
It uses the GMT (Goodman-Martinez-Thompson) correlation, the constant accepted by the large majority of Mayanist scholars and essentially all popular conversion tools, anchored to December 21, 2012 = Long Count 13.0.0.0.0. A handful of alternative correlation constants exist in the academic literature and would shift every converted date by a fixed offset of a day or more if used instead — the correlation constant is essentially a calibration choice, not something derivable from the Long Count math alone.
Did the Maya calendar actually predict the world would end in 2012?
No. December 21, 2012 marked the completion of the 13th baktun (Long Count 13.0.0.0.0), a significant cyclical milestone roughly comparable to an odometer rolling from 999,999 to 1,000,000 — the count simply continued to 13.0.0.0.1 the next day, exactly as it always had at the end of any other baktun. The '2012 apocalypse' idea was a modern popular-media interpretation, not a claim found in the Maya calendar system or in Maya inscriptions themselves.