
Mangal Shobhajatra at Pohela Boishakh in Bangladesh. It retains the historic Sanskrit names of the months, with the first month as Baishakh. The current Bengali calendar in use in the Indian states is based on the Sanskrit text Surya Siddhanta.

For Bengalis of West Bengal and other Indian states, the festival falls either on 14 or 15 April every year. The Bengali calendar in India remains tied to the Hindu calendar system and is used to set the various Bengali Hindu festivals. However, the date of the celebration, 14 April, was retained. In 2018-19, the calendar was amended again, with Falgun now lasting 29 days in regular years and to 30 days in leap ones, in an effort to more align with Western use of the Gregorian calendar. Since then, the national calendar starts with and the new year festival always falls on 14 April in Bangladesh. This was officially adopted by Bangladesh in 1987. In Bangladesh however, the old Bengali calendar was modified in 1966 by a committee headed by Muhammad Shahidullah, making the first five months 31 days long, rest 30 days each, with the month of Falgun adjusted to 31 days in every leap year. However, unlike these regions where it starts in 57 BCE, the Bengali calendar starts from 593 CE suggesting that the starting reference year was adjusted at some point. In rural Bengali communities of India, the Bengali calendar is credited to "Bikromaditto", like many other parts of India and Nepal. Buddhist texts and inscriptions created in the Pala Empire era mention "Vikrama" and the months such as Ashvin, a system found in Sanskrit texts elsewhere in ancient and medieval Indian subcontinent. Various dynasties whose territories extended into Bengal, prior to the 13th-century, used the Vikrami calendar. The term Bangabda (Bangla year) is found too in two Shiva temples many centuries older than Akbar era, suggesting that Bengali calendar existed before Akbar's time. Some historians attribute the Bengali calendar to the 7th century king Shashanka. Regardless of who adopted the Bengali calendar and the new year, states Sengupta, it helped collect land taxes after the spring harvest based on traditional Bengali calendar, because the Islamic Hijri calendar created administrative difficulties in setting the collection date. The tradition to use the Bengali calendar may have been started by Husain Shah before Akbar. It is also unclear, whether it was adopted by Alauddin Husain Shah or Akbar. According to Shamsuzzaman, it is called Bangla shon or shaal, which are Arabic (سن) and Persian (سال) words respectively, suggests that it was introduced by a Muslim king or sultan." In contrast, according to Sengupta, its traditional name is Bangabda. Īccording to Shamsuzzaman Khan, and Nitish Sengupta, the origin of the Bengali calendar is unclear. According to Shamsuzzaman Khan, it could be Nawab Murshid Quli Khan, a Mughal governor, who first used the tradition of Punyaho as "a day for ceremonial land tax collection", and used Akbar's fiscal policy to start the Bangla calendar. According to some historians, this started the Bengali calendar. Akbar asked the royal astronomer Fathullah Shirazi to create a new calendar by combining the lunar Islamic calendar and solar Hindu calendar already in use, and this was known as Fasholi shan (harvest calendar). According to some sources, the festival was a tradition introduced in Bengal during the rule of Mughal Emperor Akbar to time the tax year to the harvest, and the Bangla year was therewith called Bangabda.

This calendar was a lunar calendar, and its new year did not coincide with the solar agricultural cycles. Traditional roots Mughal origins theory ĭuring the Mughal rule, land taxes were collected from Bengali people according to the Islamic Hijri calendar.

Mughal Emperor Akbar began the celebration of Bengali New Year and officialized the Bengali calendar to ease the tax collection process.
