The Buddhist calendar is used on mainland Southeast Asia in the countries of Thailand, Cambodia, Laos, Burma (officially known as Myanmar) and Sri Lanka in several related forms. It is a lunisolar calendar having months that are alternately 29 and 30 days, with an intercalated day and a 30-day month added at regular intervals. All forms of the Buddhist calendar are based on the original version of the Surya Siddhanta, which dates to the 3rd century CE (both the original and medieval forms of the Surya Siddhanta are used by the various Hindu calendars).

Its lunisolar intercalation system generally adds seven extra months (adhikamasa) every 19 years and 11 extra days (adhikavara) every 57 years, but this is only a rough guide to the results of the actual calculations. The average year is 365.25875 days reckoned from the mahayuga of 4,320,000 years, simplified to 292,207 days every 800 years by removing a common factor of 5400 from the total days and years. This year is slightly longer than the modern sidereal year and is substantially longer than the modern tropical year. The Hindu version adds extra months and days (or removes months and days) as soon as the astronomical formulae require, whereas the southeast Asian versions delay their addition. The Thai/Lao/Cambodian version does not permit an extra day to occur within years having an extra month, whereas the Burmese/Sri Lankan version permits an extra day only in years having an extra month. Thus there are four types of lunisolar years, of 354, 355, 384, or 385 days. Even though the intercalation cycles imply a tropical year, the sidereal year that is actually used causes the 'cycles' to gradually shift throughout history.

Tsem Tulku Rinpoche (born October 24, 1965) is a tulku, a reincarnate lama of the Gelug school of Tibetan Buddhism, and the founder and spiritual guide of the Kechara House Buddhist Association in Malaysia.

Tsem Tulku is the third in the line of tulkus associated with Ganden Monastery's Shartse college and the Gyuto tantric college. His predecessors were Gedun Nyedrak,^{[unreliable source?]} a Khampa who served as Ganden Shartse's 72nd abbot; and Kentrul Thubten Lamsang, from Drikung, who died in Phari during the 1950s. Since the former came from a family which owed ties of fealty to Tsem Monastery, which housed a tooth of Tsongkhapa as a holy relic (tsem being the honorific Tibetan word for "tooth"), the name "Tsem" came to be applied to the tulku lineage; hence Tsem Tulku's appellation. ("Rinpoche" is an honorific meaning "precious," which is customarily affixed to the names of lamas.)

Tsem Tulku was born in Taipei, Taiwan to Dewa Nimbo, an Old Torghut Mongolian woman whom Tsem Tulku describes as a "princess" (she was the grand-daughter of Prince Palta, a Xinjiang government official during the Qing and Nationalist periods; and the daughter of Mingyur Wang, briefly a member of the ROC National Assembly); and Lobsang Gyatso, a Tibetan from Ngawa with ties to the Tibetan exile government who, after fleeing to Taiwan, ran a school for Tibetan refugee children. According to Tsem Tulku's website,