The Nanakshahi Calendar is named after the founder of the Sikh religion, Guru Nanak Dev.
Sikhs have traditionally recognised two eras and luni-solar calendars: the Nanakshahi and Khalsa. Traditionally, both these calendars closely followed the Bikrami calendar with the Nanakshahi year beginning on Katak Pooranmashi (full moon) and the Khalsa year commencing with Vaisakhi. The methods for calculating the beginning of the Khalsa era were based on the Bikrami calendar. The year length was also the same as the Bikrami solar year. According to Steel (2000), (since the calendar was based on the Bikrami), the calendar has twelve lunar months that are determined by the lunar phase, but thirteen months in leap years which occur every 2-3 years in the Bikrami calendar to sync the lunar calendar with its solar counterpart. References to the Nanakshahi Era have been made in historic documents. Banda Singh Bahadur adopted the Nanakshahi calendar in 1710 C.E. after his victory in Sirhand (12 May 1710 C.E.) according to which the year 1710 C.E. became Nanakshahi 241. However, according to Dilagira (1997), he "continued adopting the months and the days of the months according to the Bikrami calendar". Banda Singh Bahadur also minted new coins also called Nanakshahi.
The revised Nanakshahi calendar was designed by Pal Singh Purewal to replace the Bikrami calendar. The epoch of this calendar is the birth of the first Sikh Guru, Nanak Dev in 1469 and the Nanakshahi year commences on 1 Chet. New Year's Day falls annually on what is March 14 in the Gregorian Western calendar. The start of each month is fixed. According to Kapel (2006), the solar accuracy of the Nanakshahi calendar is linked to the Gregorian civil calendar. This is because the Nanaskhahi calendar uses the tropical year instead of using the sidereal year which is used in the Bikrami calendar or the old Nanakshahi and Khalsa calendars.
The amended Nanakshahi calendar was adopted in 1998 but implemented in 2003 by the Shiromani Gurdwara Prabhandak Committee to determine the dates for important Sikh events. The calendar was implemented during the SGPC presidency of Sikh scholar Prof. Kirpal Singh Badungar at Takhat Sri Damdama Sahib in the presence of Sikh leadership.
In 2010, the Shiromani Gurdwara Prabhandak Committee ("SGPC") modified the calendar so that the dates for the start of the months are movable so that they coincide with the Bikrami calendar and changed the dates for various Sikh festivals so they are based upon the lunar phase. This has created controversy with some bodies adopting the 2003 version, also called the "Mool Nanakshahi calendar" and others, the 2010 version. By 2014, the SGPC had scrapped the original Nanakshahi calendar from 2003 and reverted back to the Bikrami calendar entirely, however it was still published under the name of Nanakshahi. The Sikh bodies termed it a step taken under pressure from the Rashtriya Swayamsevak Sangh and Shiromani Akali Dal. There is also some controversy about the acceptance of the calendar altogether among certain sectors of the Sikh world.