The Bengali Calendar or Bangla Calendar (বঙ্গাব্দ Bônggabdô or Banggabda) is a solar calendar used in the region of Bengal. A revised version of the calendar is the national and official calendar in Bangladesh and an earlier version of the calendar is followed in the Indian states of West Bengal, Tripura and Assam. The New Year in the Bengali calendar is known as Pôhela Bôishakh.
The Bengali Era (BS) or Anno Bengal (AB, Latin for: in the year of Bengal), the Bengali year (বাংলা সন Bangla Sôn, বাংলা সাল Bangla sal) is 594 less than the AD or CE year in the Gregorian calendar if it is before Pôhela Bôishakh, or 593 less if after Pôhela Bôishakh.
The revised version of the Bengali calendar was officially adopted in Bangladesh in 1987. However, it is not followed in India where the unrevised (non-revised) traditional version continues to be followed due to occurrence of Hindu festivals based on a particular sidereal solar day.
The Bengali calendar is a solar calendar.
The origin of Bônggabdô or Bengali Year (Bangla Year) is debated, with primarily two hypotheses. The development of the Bengali calendar is often attributed to King of Gour, Shashanka as the starting date (12 or 14 April 594 CE) falls squarely within his reign. The solar calendar is based on the Surya Siddhanta, a Sanskrit astronomical text.
Another theory is that the calendar was developed by Alauddin Husain Shah (reign 1494–1519), a Hussain Shahi sultan of Bengal by combining the lunar Islamic calendar (Hijri) with the solar calendar, prevalent in Bengal.