The Bengali Era or Bangabda is used in Bangladesh, West Bengal and Tripura. It is also used in Assam where it is called the Bhaskar (Sun) Era, The era is an adaptation of the solar calendar that was introduced by Emperor Akbar in 1584 AD. Netters will recall that the Hijri era is based on the lunar calendar where the month of harvest keeps shifting from year to year. This had made it awkward to assign a fixed date for collecting taxes which became due after harvest. Akbar's calendar was the Emperor's solution to the problem.
Persians, unlike the Arabs, follow a solar calendar where the year begins on the day of vernal equinox (21st March). Akbar's calendar was based on the Persian model. Though introduced in 1584 AD, Akbar had the calendar backdated to start on 21st of March of 1556 AD which was the year he had ascended the throne. This was the year 963 in the Hijri era.
Bengal adopted Akbar's calendar with certain modifications. In 1556 AD, the Bengali calendar was assigned the year 963 to coincide with the year in Hijri era which today reads 1418. It is 1406 in the Bengali year.If we recall that a solar year is about 11 days longer than the lunar year, it is not difficult to figure out why the Hijri era has marched ahead by: [11 X (1998 - 1556)] days = 13 years in the 442 years since 1556 AD.
There is one other significant difference with Akbar's calendar which, like the Persian calendar and the Christian calendar, had months of fixed number of days. The Bengali month, on the other hand, is based on the ancient Sanskrit treatise, "Surya Siddhanta" where the months are assigned by the zodiac sign. The sun's stay under a zodiac sign varies from year to year. That is why any Bengali month can vary in length anywhere from 29 to 32 days. The sun enters the Mesh Rashi (Aries) on 15th of April, give or take a day.This marks the beginning of the Bengali year and is celebrated as the first of Baishakh.
The Bengali calendar is a prime example of the eclectic spirit that had prevailed during the rule of Emperor Akbar. It was a synthesis of features from ancient Indian calendars based on "Surya Siddhanta" with those of the Hijri calendar and the Persina calendar.