Gian Singh wrote the Twarikh Guru Khalsa in 1891. According to Singha (1996), Gian Singh was a Punjabi author born in 1822. According to The Panjab Past and Present (1993), it is Gian Singh who 'is the first to use Nanak Shahi Samvats along with those of Bikrami Samvats' in the Twarikh Guru Khalsa. Although Banda may have proclaimed this era, it cannot be traced in contemporary documents and does not seem to have been actually used for dating'. Herrli (1993) states that 'Banda is supposed to have dated his coins according to his new calendar. Banda Singh Bahadur also minted new coins also called Nanakshahi. According to Dilgeer (1997), Banda 'continued adopting the months and the days of the months according to the Bikrami calendar'. However, Singh (2008) states the date of the victory as CE. Banda Singh Bahadur adopted the Nanakshahi calendar in 1710 CE after his victory in Sirhind ( CE) according to which the year 1710 CE became Nanakshahi 241. References to the Nanakshahi Era have been made in historic documents. Kay (2011) abbreviates the Khalsa Era as KE.

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. The year length was also the same as the Bikrami solar year. The methods for calculating the beginning of the Khalsa era were based on the Bikrami calendar. 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. Sikhs have traditionally recognised two eras and luni-solar calendars: the Nanakshahi and Khalsa. The Nanakshahi Calendar is named after the founder of the Sikh religion, Guru Nanak Dev Ji. The reference epoch of the Nanakshahi calendar is the birth of Guru Nanak Dev, corresponding to the year 1469 CE. The year begins with the month of Chet, with 1 Chet corresponding to 14 March. It is based on the 'Barah Maha' (Twelve Months), a composition composed by the Sikh gurus reflecting the changes in nature conveyed in the twelve-month cycle of the year. The Nanakshahi calendar (Punjabi: ਨਾਨਕਸ਼ਾਹੀ ਜੰਤਰੀ ( Gurmukhi)) is a tropical solar calendar used in Sikhism.

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