The Bengali Calendar or ‘Bongabdo’ is a solar calendar, which is comparatively new among the others. Based on the Sanskrit text ‘Surya Siddhanta’, it is in use in some of the Indian states, particularly by the Bengali people of West Bengal, Tripura, Assam and Jharkhand. The Bengali Calendar maintains the original Sanskrit names of the months, with the first month as Baishakh. The calendar remains tied to the Hindu calendar system and is used to set the various Bengali Hindu festivals.
The Bengali calendar is directly related to the agricultural tax collection system during the Muslim rule in the country. Many historians attribute this provincial calendar to the 7th century Hindu king Sashanka, while the others maintain that, it was first developed by Alauddin Husain Shah, a Hussain Shahi sultan of Bengal, during 1494-1519. It is said that, Husain Shah combined the Hindu solar calendar with the Arabic Hijri, the lunar Islamic calendar, when he observed the practical difficulty of collecting land revenue according to the Arabic Hijri calendar.
According to some other historians, the current Bengali calendar owes its origin to the great Mughal Emperor Akbar. Realizing the urgency of reformation of the existing calendar, the Emperor requested Amir Fathullah Shirazi, one among the noted scholars of his court, to take the responsibility of making the necessary amendments in the system.In those medieval days, the regular practice was to collect the tax according to the Muslim Hijri calendar, which did not agree with the harvesting sessions of Bengal. As a result, the poor farmers had to face severe financial difficulties to clear taxes within the stipulated period. Emperor Akbar tried to solve the problem and at his insistence a new calendar was formulated, based on the lunar Hijri and the Hindu solar calendars. The consequent Bengali calendar was introduced following the harvesting season when the peasantry would be in a relatively sound financial position.
Initially, the new Bengali calendar was called as the harvest calendar or Fôsholi Shôn (ফসলী সন) and with the passing of time it came to be known as Bôngabdo (বঙ্গাব্দ).
The ‘formula’ for calculating the Bengali year, is: Islamic year at Akbar’s crowning (Hijri 963) + current Gregorian solar year (2019) - Gregorian solar year at Akbar’s crowning (1556). In other words: 963 + 2019 - 1556 = 1426.