Mayan calendar converter

Type a date, such as 21 December 2012, 2012-12-21 or 24 March 603, and add BCE for years before the common era. The result gives the Long Count and the Calendar Round, and the rows add the meaning of the day's name, the date in both the Gregorian and Julian calendars, and the Julian Day Number. The Long Count is drawn below in Maya numerals.

Swap the boxes, or just type a Long Count such as 9.12.11.5.18, to go the other way. A Calendar Round copied after it is ignored and worked out again, so you can check one against the other.

The Maya kept three cycles running side by side. The Long Count is a plain count of days from a starting day in 3114 BCE, written in five places. The Tzolk'in is a 260-day cycle that pairs a number from 1 to 13 with one of 20 day names. The Haab' is a 365-day year of 18 months of 20 days, plus 5 days at the end.

A full date gives all three: 9.12.11.5.18 6 Etz'nab' 11 Yax is the day the Palenque king K'inich Janaab' Pakal died. Wikipedia gives that as 29 August 683, in the Gregorian calendar run back before it existed.

Count the days from the starting day, then take out as many b'ak'tun as fit, then k'atun, and so on down. The tun is 18 winal, not 20, so a tun is 360 days, close to a year, and the winal place runs only from 0 to 17.

Take 24 March 603 in the Gregorian calendar, Pakal's birth. It's 1,357,100 days after the start. 1,357,100 ÷ 144,000 is 9 b'ak'tun, leaving 61,100; that's 8 k'atun, leaving 3,500; 9 tun, leaving 260; 13 winal, leaving 0 k'in. So the Long Count is 9.8.9.13.0, and the Tzolk'in and Haab' counts give 8 Ajaw 13 Pop: the date Wikipedia gives for his birth.

The Tzolk'in moves the number and the name on together each day: 1 Imix, 2 Ik', 3 Ak'b'al, and so on. After 13 the numbers start again at 1 while the names carry on, so the same pair comes back only after 13 × 20 = 260 days.

The Haab' counts days within a month from 0, the day the month is "seated", to 19. After 18 months, Pop to Kumk'u, come the five days of Wayeb', which were thought dangerous: people avoided leaving their houses.

Together they make the Calendar Round. 260 and 365 line up again only after 18,980 days, which is 73 Tzolk'in cycles and 52 Haab' years. Any Calendar Round date comes back every 52 years, which is why monuments add the Long Count.

Converting needs one fixed point: which day in our calendars was 13.0.0.0.0. Most Maya scholars use the GMT correlation, which puts it at Julian Day Number 584,283: 11 August 3114 BCE in the Gregorian calendar run backwards, or 6 September 3114 BCE in the Julian calendar. A variant, 584,285, puts every date two days later; switch Correlation to compare.

Before October 1582 there's a second choice. Writers differ on whether to give the Julian date, as people at the time wrote it, or the Gregorian date run backwards. Wikipedia's article on Pakal uses the Gregorian. Typed dates before 1582 are read as Julian unless Dates before 1582 says otherwise, and every result shows both.

Some horoscope sites call the Tzolk'in day you were born on your Maya zodiac sign. The day sign is real and this page works it out; type your birth date and the Tzolk'in row gives the name and what it means. The Calendar Round is still kept by many communities in the Guatemalan highlands. The personality readings that horoscope sites attach to each sign aren't part of what the inscriptions record, so this page leaves them out.