The Bikrami calendar, also called Vikrami calendar or sometimes Hindu calendar, is named after king Vikramaditya and starts in 57 B.C. The Vikrami era, or Vikrami-samvat, is notable because many ancient and medieval era inscriptions use it. However, in early inscriptions the term Vikrami-samvat is not used, rather the same calendaring system is found by other names such as Krita and Malava.
The Vikrami era ancient calendar has been historically used by Hindus and Sikhs. It is one of the several regional Hindu calendars that have been in use on the Indian subcontinent, and it is based on twelve synodical lunar months and 365 solar days. The lunar new year starts on the new moon in the month of Chaitra. This day, known as Chaitra Sukhladi, is a restricted holiday in India.
The Vikrami calendar is similar in conceptual design to the Jewish calendar, but different from the Gregorian calendar. Unlike Gregorian calendar which adds additional days to lunar month to adjust for the mismatch between twelve lunar cycles (354 lunar days) and nearly 365 solar days, the Vikrami and Jewish calendars maintain the integrity of the lunar month, but insert an extra full month by complex rules, every few years, to ensure that the festivals and crop related rituals fall in the appropriate season. This Indian system of calendar keeping is one of the luni-solar calendar systems innovated in ancient human cultures. Early Buddhist communities of India adopted the ancient Indian calendar, later Vikrami calendar and then local Buddhist calendars. Buddhist festivals continue to be scheduled according to a lunar system.
The Vikrami samvat (Bikrami Samvat system) has been in use in the Indian subcontinent since ancient times, and remains in use by the Hindus in north, west and central India as well as Nepal. In south India, and some parts of east and west India such as Assam, Bengal and Gujarat, saka era has been widely used. With the arrival of the Islamic rule era, the Hijri Islamic calendar became the official calendar of various Sultanates and the Mughal Empire. During the colonial rule era of the Indian subcontinent, the Gregorian calendar was adopted and it is commonly used in the urban areas of India and Nepal. The predominantly Muslim countries of Pakistan and Bangladesh use the Islamic calendar since 1947, but older texts variously include the Bikrami and Gregorian calendar systems. In 2003, the India-based Shiromani Gurdwara Parbandhak Committee of Sikhism adopted the Nanakshahi calendar, a move that continues to be debated. The Vikrami calendar is the official calendar of Nepal.