The Buddhist calendar is luni-solar, a combination of the lunar and solar calendars. It is based on the original third century Surya Siddhanta. The months in this calendar alternate between 29 and 30 and at regular intervals, an intercalated day and a 30-day month added to it. The people living in the Southeast Asian countries mainly use the Buddhist calendar. These countries include Cambodia, Laos, Thailand, and Myanmar (formerly Burma). There are mainly four versions of the Calendar of the Buddhists.
The lunisolar intercalation system of the calendar has seven extra months (adhikamasa), every 19 years and 11 extra days (adhikavara), every 57 years. On an average, a year consists of 365.25875 days, deemed from the mahayuga of 4,320,000 years. While the Hindu version makes additions and deduction the moment the astronomical formulae require, the Southeast Asian one delays it. Then, we have the Thai/Lao/Cambodian version in which there cannot be an extra day in the year having an extra month.
The Burmese version is exactly the opposite. It permits an extra day only in the years having an extra month. Thus, each of the four versions of the calendar has different days, i.e. 354, 355, 384, or 385 days respectively. The names of the month are in Sanskrit, namely Chaitra, Vaisakha, Jyestha, Ashadha, Shravan, Bhadrapada, Asvina, Kartik, Maragasirsha, Pausha, Magha and Phalguna. The old Burmese month names were Tagu, Kason, Nayon, Wazo, Wagaung, Tawthalin, Thadingyut, Tarzaungmon, Natdaw, Pyatho, Tabodwe and Tabaung. There were/are mainly four eras in the Buddhist calendars, namely…
Anchansakarat – From 10 March 691 BC
Buddhasakarat – Buddhist Era or BE, 11 March 545 BC
Mahasakarat – 17 March 78 (same as the Saka Era in India)
Chulasakarat – 22 March 638
Since all years are elapsed/expired/complete years, their epochal year is not year 1, but year 0.