The Bengali calendar is a
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
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.
All theories agree that the
Akbar (reign 1556 – 1605) was instrumental in "promulgating" the Bengali calendar. Akbar modified, developed and re introduced the Bengali Calendar in order to make tax collection easier in Bengal. The calendar was then called as Tarikh-e-Elahi (তারিখ-ই ইলাহি). Akbar changed the practice of agricultural tax collection which had been according to the Islamic calendar and ordered an improvement of the calendar systems, because the
lunar Islamic calendar did not agree with the harvest sessions and the farmers faced severe difficulties in paying taxes out of season. Some sources credit the idea to the finance minister of Akbar,
Akbar's royal astronomer
Fathullah Shirazi developed the Bengali calendar, by synthesizing the Lunar Islamic and
Solar Hindu calendars. The calendar started with the Islamic calendar value, but the Sanskrit month names were used from the earlier version.
 The distinctive characteristic of the Bengali year was that rather than being a lunar calendar, it was based on a
union of the solar and lunar year. This was essentially a great promotion as the solar and lunar years were formulated in very diverse systems.
Primarily this calendar was named as "Fasli Sôn" and then "Bônggabdô". The Bengali Year was launched on 1584 AD or 992 AH (Hijri), but was dated from the year 1556 AD or 963 AH. This was the day that Akbar defeated
Hemu in the
clash of Panipat to ascend the throne. The month of
Muharram in the year 963 AH was equal to the month of
Boishakh in the Bengali calendar, and so Boishakh month has continued to be the first month of the Bengali calendar.
In the "Tarikh-e-Elahi" version of the calendar, each day of the month had a separate name, and the months had different names from what they have now. Akbar's grandson
Shah Jahan reformed the calendar to use a seven-day week that begins on Sunday, and the names of the months were changed at an unknown time to match the month names of the existing