Maya Calendar Round Calculator for Any Date

It uses the widely adopted Goodman-Martinez-Thompson correlation constant of 584283 and performs the calculation with integer calendar arithmetic, so the result does not depend on a device clock, local timezone, daylight-saving rules, or network data. The response shows the numbered Tzolkin day, the Haab day and month, their combined Calendar Round label, and the Julian day number used in the conversion, making the result easy to inspect or reproduce.

What the Maya Calendar Round represents

The Calendar Round combines two repeating Maya calendar cycles. The Tzolkin is a 260-day cycle formed by pairing thirteen day numbers with twenty day names. Because the number and name sequences advance together, a particular Tzolkin designation returns after 260 days. The Haab is a 365-day civil cycle made from eighteen months of twenty days followed by Wayeb, a short final period of five days. A combined Tzolkin and Haab position repeats after 18,980 days, or 52 Haab years. This calculator reports both positions rather than treating either one as a complete long-term date. That distinction matters: a Calendar Round label identifies a position inside a repeating cycle, not one unique day across all history. The response therefore also includes the submitted ISO date and its Julian day number. Those fields make the conversion auditable and prevent the repeating label from being mistaken for a unique Long Count date. Spellings follow common English Mayanist forms, including Ajaw, Kankin, and Wayeb.

How the conversion stays deterministic

Enter a Gregorian date in exact YYYY-MM-DD form. The calculator validates the month, the day, and Gregorian leap-year rules before doing any conversion. It then converts the date to an integer Julian day number with proleptic Gregorian arithmetic. No JavaScript Date object is constructed, so a browser in Tokyo, a server in UTC, and a laptop in New York all follow the same path and obtain the same value. The Maya position is anchored with the Goodman-Martinez-Thompson correlation constant 584283, commonly abbreviated GMT. At the correlation origin, the cycle offsets correspond to 4 Ajaw and 8 Kumku; modular arithmetic advances those offsets to the requested day. Negative remainders are normalized explicitly, which also keeps dates earlier than the correlation origin well defined within the supported Gregorian range. The output names the selected correlation because correlation choice is an interpretive premise, not an invisible implementation detail. If a publication uses another correlation, its result can differ even though both calculations are internally consistent.

Reading and using the result responsibly

Read the calendar_round field as Tzolkin first and Haab second. For example, a value such as 4 Ajaw / 3 Kankin means Tzolkin number 4 with day name Ajaw, paired with day 3 of the Haab month Kankin. The nested tzolkin and haab objects are better for software that needs separate fields, while the combined string is convenient for display, notes, or a citation draft. Use julian_day_number when comparing this result with another conversion tool: matching day numbers but different Maya positions usually indicate a different correlation or offset convention. The calculation applies the proleptic Gregorian calendar throughout the supported range, including dates before a country historically adopted the Gregorian calendar. That makes computation uniform but may differ from a date written in a historical Julian-calendar source. This tool computes calendrical positions; it does not authenticate inscriptions, infer a Long Count, resolve archaeological debates, or claim a cultural interpretation. For research, record the ISO input, GMT 584283 correlation, and returned fields together so another reader can reproduce exactly what was calculated.