The calendar used by the Punjabi people varies by religions. Historically, the Punjabi Sikhs and Hindus have used the Indian Bikrami (Vikrami) calendar which started in 57 B.C. with King Vikramaditya. Punjabi Muslims use the Arabic Hijri calendar. Some festivals in Punjab, Pakistan are determined by the Punjabi calendar, such as Muharram which is celebrated twice, once according to the Muslim year and again on the 10th of harh. The Bikrami calendar is the one the rural (agrarian) population follows in Punjab, Pakistan.[note 1]
In Punjab though the solar calendar is generally followed, the lunar calendar used is purnimanta. The lunar month is calculated from the ending moment of the full moon: the beginning of the dark fortnight. Chaitra is considered to be the first month of the lunar year. The lunar year begins on Chet Sudi: the first day after the new moon in the month of Chet. This means that the first half of the purnimanta month of Chaitra goes to the previous year, while the second half belongs to the new Lunar year.
The regional new year is observed on Vaisakhi which is determined by the solar calendar. The day is considered from sunrise to next sunrise and for the first day of the solar months, the Orissa rule is observed: day 1 of the month occurs on the day of the sankranti (known as sangrand in Punjabi).