Оңтүстік-Шығыс Азия буддалық күнтізбесі

Set of lunisolar calendars used in SE Asia

The Buddhist calendar is a set of lunisolar calendars primarily used in Tibet, Cambodia, Laos, Myanmar, Bangladesh, India, Sri Lanka, Thailand and Vietnam as well as in Malaysia and Singapore and by Chinese populations for religious or official occasions. While the calendars share a common lineage, they also have minor but important variations such as intercalation schedules, month names and numbering, use of cycles, etc. In Thailand, the name Buddhist Era is a year numbering system shared by the traditional Thai lunar calendar and by the Thai solar calendar. The Southeast Asian lunisolar calendars are largely based on an older version of the Hindu calendar, 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.

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.)

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.

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.

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. 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.

The lunisolar calendar is used to mark important Buddhist holidays. Many of the holidays are celebrated as public holidays. Buddhist calendar dateInternational datePublic holiday inNotes Full moon of Phussa January Sri Lanka Duruthu Poya: Commemorates the first visit of the Buddha to Sri Lanka Full moon of Māgha February Cambodia, Laos, Sri Lanka, Thailand Magha Puja in Cambodia, Laos, Thailand and known as Navam Poya in Sri Lanka Full moon of Phagguṇa March Laos, Myanmar, Sri Lanka Boun Pha Vet (Laos), Tabaung Festival (Myanmar), Medin Poya (Sri Lanka) Almost always in Citta, sometimes in Vesākha 13–17 April (varies by country) Cambodia, Laos, Myanmar, Sri Lanka, Thailand Songkran (Southeast Asian New Year) Traditionally, the New Year's Day is marked when the Sun enters Aries but the day is now fixed in most countries; Myanmar still follows the tradition. It also marks the beginning of the next Buddhist calendar animal zodiac year for certain countries. Full moon of Citta April Sri Lanka Bak Poya: Commemorates the second visit of the Buddha to Sri Lanka Full moon of Vesākha May Cambodia, Laos, Thailand, Sri Lanka, Myanmar, Malaysia, Singapore Buddha Day (Vesak) Full moon of Jeṭṭha June Sri Lanka Poson Poya: Commemorates introduction of Buddhism to Sri Lanka Full moon of Āsāḷha July Cambodia, Laos, Myanmar, Thailand, Sri Lanka Vassa Esala Poya (Sri Lanka) Asalha Puja (Thailand) Full moon of Sāvaṇa August Sri Lanka Nikini Poya Full moon of Poṭṭhapāda September Laos, Sri Lanka Binara Poya (Sri Lanka) Full moon of Assayuja October Cambodia, Laos, Myanmar, Sri Lanka End of Vassa Boun Suang Huea (Laos); Thadingyut Festival (Myanmar); Vap Poya (Sri Lanka); Wan Ok Phansa (Thailand) Full moon of Kattika November Laos, Myanmar, Sri Lanka, Thailand, Cambodia That Luang Festival (Laos); Tazaungdaing Festival (Myanmar); Il Poya (Sri Lanka); Loi Krathong (Thailand); Bon Om Touk (Cambodia) Full moon of Māgasira December Sri Lanka Undhuvap Poya (Sri Lanka)

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