The Bengali calendar (বঙ্গাব্দ Bônggabdo or বাংলা সন Bangla Shôn) or Bangla calendar is a traditional solar calendar used in Bangladesh and India's eastern states of West Bengal, Assam and Tripura. The year begins on Pôhela Boishakh, which falls on 14 April in Bangladesh and 15 April in India. In Assam, this corresponds to Bhaskar Era, named after the Kamarupa king, Bhaskara Varman.
The current Bengali year is 1415. The Bengali year is always 593 less than the year in the Gregorian calendar of the Christian Era or Anno Domini era or Common Era or Current Era for the period after Pôhela Boishakh. However, the Bengali calendar is 594 less than the Gregorian calendar if it is before Pôhela Boishakh.
The new Fôsholi Shôn was introduced on 10/11 March 1584, but was dated from Akbar's accession to the throne in 1556. The new year subsequently became known as বঙ্গাব্দ Bônggabdo or বাংলা সন Bangla Shôn ("Bengali year").
In a different interpretation, King Shashanka of Ancient Bengal, who ruled approximately between 600 AD and 625 AD, is credited with starting the Bengali era. Shashankya was the sovereign king of Bengal at the start of seventh century. Much of today’s Indian states of Bengal, Bihar, and Orissa was under his kingdom. The prevailing reason is that the year cannot start as 963 B.S. (Bangla Shôn) in synchrony with 963 Hijra. The Bengali Era must have begun before that and Akbar took over form this point on. According to this the starting point of Bengali Era was AD 593/594. By the time of reign of Akbar in AD 1556 the Bengali Era 963 B.S. had been in synchrony with then used 963 Hijra era. Because of the practical advantages of using a solar year, Akbar started using the Bengali era as the official calendar for collecting taxes. Extrapolating further back to the starting point of Bengali era it could be stated that it started on Monday, 12 April 594 in Julian Calendar and Monday, 14 April 594 in proleptic Gregorian calendar.
During the reign of the Mughals, the Bengali Calendar was officially implemented throughout the empire. Apart from Bengal, however, the calendar was abandoned with the end of Mughal rule.
| কাল/ঋতু Kal/Ritu|
The month names in the initial Bengali calendar were different from those used in the modern version. Originally, the months were known under the names of the Persian calendar as Farwadin, Ardi, Vihisu, Khordad, Teer, Amardad, Shahriar, Aban, Azur', Dai, Baham and Iskander Miz.
In the Bengali calendar, the day begins and ends at sunrise , unlike in the Gregorian calendar, where the day starts at midnight.
The length of a year in the Bengali calendar, as in the Gregorian calendar, is counted as 365 days. However, the actual time taken by the earth in its revolution around the sun is 365 days 5 hours 48 minutes and 47 seconds. To make up this discrepancy, the Gregorian calendar adds an extra day, to make a leap year, to the month of February every fourth year (except in century years which are not divisible by 400). The Bengali calendar, which was based on astronomical calculations, did not make this extra leap year adjustment. Bengali months, too, were of different lengths. To counter this discrepancy, and to make the Bengali calendar more precise, the following recommendations of the Bangla Academy are followed:
The revised calendar is officially adopted in Bangladesh in 1987. However, it is not followed in the neighbouring state of West Bengal, India, where the old calendar continues to be followed.
In West Bengal, India, the Bengalis follow a sidereal solar calendar unlike the tropical solar calendars, such as the reformed Bengali and Gregorian Calendars. The mathematical difference between the sidereal and the tropical calendars amounts to the difference of starting the new year in Bangladesh and West Bengal, India. Because of this the length of the months are also not fixed in the Bengali sidereal calendar, but rather are based on the true movement of the sun.
Although the sidereal solar calendar is being followed in West Bengal, India, the number of days in the months are determined by the true motion of the Sun through zodiac. In this calendar, seven is subtracted from the year number the result is divided by 39. If after the division the remainder becomes zero or could be divided by 4, the year is then designated as a leap year and contains 366 days with the last month Choitro taking 31 days. There are 10 leap years in every 37 years, although an extraordinary revision may be required over a long time.
In everyday use, the Bengali Calendar has been largely replaced by the Gregorian Calendar in Bengali-speaking regions, although it is still essential for marking holidays specific to Bengali culture (e.g. Pôhela Boishakh, Durga Puja, etc.), and for marking the seasons of the year, and is thus recognized by the Bangladeshi government for the observation of public holidays. Almost every Bengali- and English-language newspaper in Bangladesh and West Bengal prints the day's date according to the Bengali Calendar alongside the corresponding date of the Gregorian Calendar. Many newspapers in Bangladesh also add a third date, following the Islamic Hijri Calendar. Thus, it is quite common in Bangladesh to find the date written three times (e.g. "25 Falgun 1412, 17 Muharram 1427, 27 February 2006") under the newspaper title.