Buddhist calendar

The calculation methodology of the current versions of Southeast Asian Buddhist calendars is largely based on that of the Burmese calendar, which was in use in various Southeast Asian kingdoms down to the 19th century under the names of Chula Sakarat and Jolak Sakaraj. The Burmese calendar in turn was based on the "original" Surya Siddhanta system of ancient India (believed to be Ardharatrika school). One key difference with Indian systems is that the Burmese system has followed a variation of the Metonic cycle. It is unclear from where, when or how the Metonic system was introduced; hypotheses range from China to Europe. The Burmese system, and indeed the Southeast Asian systems, thus use a "strange" combination of sidereal years from the Indian calendar in combination with the Metonic cycle better for tropical years. Epoch Ceylonese Hinayana tradition starts Buddha Varsa on 16 Apri 545 BCE. In all Theravada traditions, the calendar's epoch (foundational moment) was the day in which the Buddha attained parinibbāna. However, not all traditions agree on when it actually took place. In Burmese Buddhist tradition, it was 13 May 544 BCE (Tuesday, Full moon of Kason 148 Anjanasakaraj). In Thai Buddhist tradition, it was 11 March 544 BCE (–543), the date which the current Thai lunisolar and solar calendars use as their epochal date. Yet, the Thai calendars for some reason have fixed the difference between their Buddhist Era (BE) numbering and the Common Era (CE) numbering at exactly 543 years. In Myanmar, the difference between BE and CE can be 543 or 542 for CE dates, and 542 or 541 for BCE dates, depending on the month of the Buddhist Era (as the Buddhist calendar straddles the Gregorian calendar — during the entire period from 1739 to 2000 CE, this is from April to April). (The Tibetan calendar (Phugpa system) counts years from the arrival of the Kālacakra Tantra in Tibet (1027 CE), resulting in a much lower year number than the Theravada BE.) , the Buddhist new year begins on 21 May 2026 everywhere except Thailand and Tibet. It begins on 1 January 2026 in Thailand and on 18 February 2026 in Tibet (when the new year will become 2153). Month Types The calendar recognizes two types of months: synodic month and sidereal month. (The Burmese calendar also recognizes a solar month called Thuriya Matha, which is defined as 1/12th of a year. But the solar month varies by the type of year such as tropical year, sidereal year, etc.) Waxing and waning The days of the month are counted in two halves, waxing and waning. The 15th of the waxing is the civil full moon day. The civil new moon day is the last day of the month (14th or 15th waning). Because of the inaccuracy of the calendrical calculation systems, the mean and real (true) New Moons rarely coincide. The mean New Moon often precedes the real New Moon. Year The Buddhist calendar is a lunisolar calendar in which the months are based on lunar months and years are based on solar years. One of its primary objectives is to synchronize the lunar part with the solar part. The lunar months, normally twelve of them, consist alternately of 29 days and 30 days, such that a normal lunar year will contain 354 days, as opposed to the solar year of ~365.25 days. Therefore, some form of addition to the lunar year (of intercalation) is necessary. The overall basis for it is provided by cycles of 57 years. Eleven extra days are inserted in every 57 years, and seven extra months of 30 days are inserted in every 19 years (21 months in 57 years). This provides 20819 complete days to both calendars. This 57-year cycle would provide a mean year of about 365.2456 days and a mean month of about 29.530496 days, if not corrected. As such, the calendar adds an intercalary month in leap years and sometimes also an intercalary day in great leap years. The intercalary month not only corrects the length of the year but also corrects the accumulating error of the month to extent of half a day. The average length of the month is further corrected by adding a day to Nayon at irregular intervals—a little more than seven times in two cycles (39 years). The intercalary day is never inserted except in a year which has an intercalary month. Burmese The Burmese calendar year consists of 354, 384 or 385 days. Note: The Arakanese calendar adds the intercalary day in Tagu, not in Nayon. Cambodian, Lao and Thai The Cambodian, Lao and Thai lunisolar calendars use a slightly different method to place the intercalary day. Instead of it in a leap year as in the Burmese system, the Thai system places it in a separate year. Thus, the Thai small leap year has 355 days while the Thai great leap year has 384 days. Thailand and Cambodia no longer use the traditional lunisolar calendar to mark the New Year's Day. Cycle The Cambodian, Lao and Thai systems give animal names to the years from a cycle of 12. The practice also existed in Burma in the Pagan period but later died out. The Cambodian calendar also maintains a 10-year naming cycle (numbered one to ten). Cambodians use multiple systems to identify a given year. For instance, 2017 is identified as 2561 Buddhist Era, the year of Rooster, Nuppasak (Year 9). The Thai lunar calendar also uses a similar numbered 10-year cycle. Each number in the cycle corresponds to the last digit of the year in the Chula Sakarat calendar. ==Accuracy==

The Southeast Asian Buddhist calendars use lunar months but try to keep pace with the solar year, by inserting intercalary months and days on the Metonic cycle (in the case of the Burmese calendar, on a modified Metonic cycle). However, the solar year as defined by the Buddhist calendars is really a sidereal year, which is nearly 24 minutes longer than the actual mean tropical year. Therefore, like all sidereal-based calendars, the lunisolar calendars are slowly drifting away from the seasons. The calendars are drifting one day approximately every 60 years and 4 months. The accumulating drift against the seasons means the New Year's Day which used to fall on 22 March (near the vernal equinox) in 638 CE now falls on 17 April in 2013 CE. There is no known internationally concerted effort to stop this drift. Thailand has moved its "Buddhist Era" to the Gregorian calendar under the name of Thai solar calendar. In Myanmar, Burmese calendarists have tried to deal with the issue by periodically modifying the intercalation schedule in the Metonic cycle. One major downside of this approach is that it is not possible to publish future calendars more than a few years (often even a year) ahead. ==History==

The Buddhist Era was first introduced to Southeast Asia along with Buddhism in the early centuries CE. It was not a separate calendar but simply a year numbering system that employed the organization and calculation methods of the prevailing lunisolar calendars in use throughout the region. In the early centuries CE, the reference civil calendar of the Buddhist calendar prevalent in Southeast Asia was the Saka Era (Mahāsakaraj Era), which is said to have been adopted by the Pyu state of Sri Ksetra in 80 CE. The Saka Era was gradually replaced by the Burmese Era or Culāsakaraj, first in Myanmar in 640 CE, and in other Theravada kingdoms of Southeast Asia between the 13th and 16th centuries. The earliest use of the Burmese calendar in lands part of present-day Thailand dates to the mid-13th century. Ayutthaya adopted the Burmese calendar in the 16th century. Theravada Buddhist tradition also recognizes pre-Buddhist Anjana Sakaraj (Añjana's Era) since the events of the Buddha's life are recorded in that era.). The Thai Buddhist Era was further realigned to the Gregorian calendar on 6 September 1940 when Prime Minister Phibunsongkhram decreed 1 January 1941 as the start of the year 2484 BE. As a result, the Year 2483 was only 9 months long, and the Thai Buddhist Era equals that of the Common Era plus 543 years. ==Current usage==

The lunisolar calendar is used to mark important Buddhist holidays. Many of the holidays are celebrated as public holidays. ==Computer support==

The Thai-style "Buddhist calendar", which is the Gregorian calendar with the Buddhist era, is supported in Java 8, iOS, and macOS. ==See also==