仏滅紀元
The exact date of Buddha's Birthday is based on the Asian lunisolar calendars and is primarily celebrated in Baisakh month of the Buddhist calendar and the Bikram Sambat Hindu calendar. This is the reason behind the term Vesak. In modern-day India and Nepal, where the Historical Buddha lived, it is celebrated on the full moon day of the Vaisakha month of the Buddhist calendar. In Theravada countries following the Buddhist calendar, it falls on the full moon, Uposatha day, typically in the 5th or 6th lunar month. In China and Korea, it is celebrated on the eighth day of the fourth month in the Chinese lunar calendar. The date varies from year to year in the Western Gregorian calendar, but usually falls in April or May. In leap years it may be celebrated in June. In Tibet, it falls on the 7th day of the fourth month of the Tibetan calendar.