Shabad Kirtan: “Nanak Tina Basant Hai (Raag Basant) by Bhai Jasbir Singh Pounta Sahib Wale. Thank you Ji for the wonderful kirtan. (source: Sukhjit Sukhi on YouTube)

By Harnaak Singh

We will now continue with the study of calendars.  We will start our discussion on the Bikrami Calendar on which Sikh Gurpurabs and other key Sikh events are presently and prior to 2003 were based on.  Then we will look briefly at the Indian Saka and the Purewal’s Mool Nanakshahi calendar.  

Note that the Purewal’s Mool Nanakshahi was in use for Sikh Gurpurabs and key Sikh events from 2003 to 2014.

Note that we will continue with the figure number from Part 3.  

Recall that the softwares we use are Star Fisher and Jagannath Hora.  These programs are available for free download at



Bikrami or Vikrami Calendar

It is claimed that this calendar was started by King Vikrami.  However Vikrami-samvat was not found in early inscriptions but the calendaring systems referred to as Krita and Malava.  So the claim that King Vikrami started this calendar may not be totally appropriate. 

The Bikrami calendar is similar in design to the Jewish calendar.  

Bikrami calendar uses nirayana (sidereal) method to position the planets (unlike Gregorian which uses sayana (tropical) method to position the planets).  

In nirayana (sidereal) method, the zodiac is aligned with 27 constellations, or fixed star groups.  Aries, the first sign of the zodiac, aligns with the first constellation, called Aswini (Part of Aries Constellation).  

The earth’s equator shifts backward through the signs of the zodiac at the rate of about 51″ (seconds) of longitude per year. This is called “precession of the equinoxes.”  Because of this phenomenon, the theoretical Aries of the western zodiac drifts further and further from the Aries used by Vedic astrologers; at the rate of about 1 degree every 72 years.  We have discussed this shift and its drift with the seasons in Parts 2 and 3.

Figure 21: Movement of the constellation cylinder – precession 

Zodiac-months HR Precession


Bikrami calendar is a lunisolar calendar.  It is based on 12 synodical solar months and 365 solar daysThe calendar starts with lunar/solar month CHET which is the start of SPRING.  The day on which CHET starts depends on the version of calendar used.  The start of CHET can be 

  • the day following full moon (purnimata) before March equinox
  • the day following new moon (amanta) before the March Equinox
  • the day the sun enters the particular zodiac sign during (Sangrand) March.

Though the nirayana (sidereal) calculation (e.g. used Jagannatha Hora and most Indian calculations) does not directly determine the equinox, it is known that the equinox falls on 20th /21st March.  This date can also be estimated by the fact that day and night being almost equal during equinox. 

Actually information about the solar months is spelt out in the Surya Siddhanta (which dates back to 400AD) clauses for example Chapter 1 Clauses 12 (a solar day is between sunrises), 13 (month begins when Sun enters a new zodiac sign) and 28 (there are 12 signs of 30 degrees to make a complete circle) and Chapter 17 Clauses 7 to 10 (defines the equinoxes and solstices).  Chapter 12 Clauses 57, 58, 61, 62 (about day and night and equal day and night at the equinoxes).  It is interesting to note here that these clauses actually are related to Sayana (Tropical) concepts not Nirayana (Sidereal) concepts though Indian computation is nowadays practically Nirayana (Sidereal).  

The Bikrami day, in fact possibly for all Indian calendars, is from sunrise to sunrise as spelt out in the Surya Siddhanta (Chaptaer 1 Clause 12).

The ensuing calculations are done using Jagannath Hora for nirayana (sidereal) and Star Fisher for sayana (tropical).  The dates are all Gregorain dates.

Let us consider the start of CHET in 2018 as an example.  

The commencing of CHET is as follows; based on 

  • full moon (purnimata) CHET starts on 2-March-2018 AD
  • new moon (amanta) CHET starts on 18-March-2018 AD 
  • zodiac sign (sangrand) CHET starts on 14-March-2018 AD.

Considering the solar month based on zodiac sign (this is what we call Sangrand), CHET starts with the sun entering the particular zodiac sign (in 2018 it is Pisces) based on nirayana year (sidereal year).  Figure 22 shows the Indian months together with the Nirayana and Tropical calculation of the months according to transition into zodiac signs as an example.  Note months JETH (2018) and CHET (2019) fall a day earlier (yellow highlight) because the Indian day is that being between sunrises (Surya Siddhanta Chapter 1 Clause 12).  Also note the shift in zodiac signs (see column under Zodiac and compare sign in the same row for nirayana and tropical e.g. in CHET nirayana sign is Pisces and tropical sign is Aries) according to the nirayana (sidereal) and the tropical.  In 2018 CHET occurs in PISCES based on nirayana (sidereal) calculation and straddles PISCES and ARIES in the tropical calculation.  The number of days in each month is also shown in the Figure.

Figure 22: Indian months shown with Sidereal and Tropical zodiac signs 2018-2019

22 Indian Months 2018-9

In year Nanakshahi 1, 1469-70 AD, CHET started on March 6th (when sun entered zodiac sign Pisces).  

Compare this with CHET starting on March 14 in 2018-19.  

In year Nanakshahi 1000 (2469-70 AD) CHET will start on March 20th (when the sun enters zodiac sign Pisces)Notice how the date shifts with time.  

In year Nanakshahi 2000 (3469-70) CHET will start on 5th March (when zodiac sign enters Aquarius); this is assuming that CHET stays within March to keep a certain degree of match with the seasons.  If this is not done then CHET will fall on 3rd April (when the sun enters zodiac sign Pisces).  

Let us put this in a table for easy comparison.  I have included, additionally, the start date of 1st March in Nanakshahi 1716, 3185-86 Gregorian.

Year Nanakshahi

Year Gregorian Start date of CHET (Gregorian) Zodiac Sign


1469-1470 AD 6th March Pisces


2018-2019 AD 14th March



2469-2470 AD 20th March



3185-3186 AD 1th March


2000 3469-3470 AD 5th March



(no month adjustment)

3469-3470 AD 3rd April


It is very important to appreciate this shift and note that the calculation is using the solar month not lunar months.  The SANGRAND is based on solar month which starts on the day when sun moves into a zodiac sign.  The lunar months are not used to mark the months if SANGRAND is used as the month marker.

The Bikrami calendar adds an extra intercalary month or leap month every few years to ensure the festivals and crop related rituals fall in the appropriate season.  The Bikrami calendar served as an agrarian calendar in Punjab.  

Muhammad A Z Mughal did a study (2014) of calendars in relation to social aspects in Punjab for his PhD at Durham University UK.  This study included the impact of calendars on seasons and crops.  A table, Figure 23 from Durham University paper “Calendars Tell History: Social Rhythm and Social Change in Rural Pakistan” by Muhammad Aurang Zeb Mughal links the months to seasons this.  Figure 24 from the same paper links months to crops.  Note that, intercalary month, is relevant for a calendar that uses lunar months to fit into a solar year.  It is not relevant if Sangrand is used to mark the months.  However it may be a consideration if the moon phases are used to mark events.

Figure 23: Months and corresponding seasons

23 Months and seasons

Figure 24: Months and corresponding crops

24 Months n crops

Intercalary or leap month 

The lunar year is about 11 days shorter than the solar year.  A leap month or intercalary month (the thirteenth month in that year) is added about every three years.  This synchronizes the lunar calendar with the sidereal solar year.

The leap month, called “adhik maas” or “purushottam maas” is added when the lunar month starts before the sun has moved to a new zodiac sign.  It falls every 32.5 month on the average.

Note that a month can also be omitted.  In rare cases, when the sun traverses the whole zodiac sign during the course of the lunar month, the month is omitted.  This happens once in 140 years or once in 190 years.  

Note that this part is relevant for a calendar that uses lunar months to fit into a solar year.  It is not relevant if Sangrand is used to mark the months.  

Saka calendar 

(source: Wikipedia)

The Saka calendar is the Indian National calendar.  Saka era starts with vernal equinox of 78 AD.  Saka year starts with CHET on 22 March yearly except 21 March for leap year.

Saka calendar months/days 

  Month (Sanskrit) Day Length Start date (Gregorian) Tropical zodiac
1 Chaitra 30/31 March 22/21 Aries
2 Vaishākha 31 April 21 Taurus
3 Jyēshtha 31 May 22 Gemini
4 Āshādha 31 June 22 Cancer
5 Shrāvana 31 July 23 Leo
6 Bhaadra 31 August 23 Virgo
7 Āshwin 30 September 23 Libra
8 Kārtika 30 October 23 Scorpio
9 Agrahayana 30 November 22 Sagittarius
10 Pausha 30 December 22 Capricorn
11 Māgha 30 January 21 Aquarius
12 Phalguna 30 February 20 Pisces

The Saka calendar months broadly follow the tropical calculation instead of the sidereal calculation.  Note that the Gregorian date of March 20/21 is the vernal equinox and when the sun moves into Aries.  However the month change dates generally may not fall on the day of entry to a new zodiac sign.  Years are counted in the Saka era, in which the first year is year 78 of the Common Era

LEAP YEAR RULE:  The Saka calendar follows the leap year rule of the Gregorian Calendar but the leap day is added to Chaitra (CHET).

 Purewal’s Mool Nanakshahi calendar

(sources: Wikipedia and “New Nanakshahi Calendar by Pal Singh Purewal published in Understanding Sikhism – The Research Journal)

The Mool Nanakshahi calendar is the design of Pal Singh Purewal.  This calendar was introduced for use by the Sikh Panth in 2003.  In 2014, due to some problems it was shelved and replaced by the Bikrami calendar that was in use prior to 2003.  

In future article/s we will perform a detailed analysis of the Purewal’s Mool Nanakshahi calendar.  

Nanakshahi era starts in 1469 AD, the year of birth of Sri Guru Nanak Dev Ji.  Note that Nanakshahi year was already in use prior to the introduction of the Purewal’s Mool Nanakshahi calender Purewal used this name for his calendar.  

Purewal’s Mool Nanakshahi year starts with CHET on 14 March yearly.

Purewal’s Mool Nanakshahi calendar months/days are shown in Figure 25.  Note that this figure is an extract from Wikipedia.  

Figure 25: Months according to Purewal’s Nanakshahi Calendar

25 Purewal

Purewal’s Mool Nanakshahi calendar months claims to broadly follow the tropical calculation instead of the sidereal calculation.  It is not clear as to how the beginning date of CHET is chosen, but it appears to be in accordance with Sangrand which is the movement of sun into a zodiac sign based on sidereal calculation in the year Purewal prepared the calendar (1999).   

The Purewal’s Mool Nanakshani calendar has some elements of the Indian Saka calendar in that the number of days in a month are chosen as per Saka calendar, except that the start date of the month and leap day month is different.  

Years are counted in the Nanakshahi era, which starts its year 1 in the year 1469 of the Common Era

LEAP YEAR RULE:  The Purewal’s Mool Nanakshahi calendar follows the leap year rule of the Gregorian Calendar and the leap day is added to month PHAGUN.

Important Sikh dates

The key Sikh dates are (from Wikipedia) as follows.

Figure 26: Fixed Sikh Festivals according to Purewal’s Nanakshahi Calendar (from Wikipedia)

26 Purewal

Figure 27: Movable Dates according to Purewal’s Nanakshahi Calendar (from Wikipedia)

27 Purewal

Please do not hesitate to ask for clarification if you would like to understand further any of the concepts or information presented above.

We will stop here and continue with our discussion on analysis of the Purewal’s Nanakshahi calendar in the next post.

Thank you for reading.  Hope you enjoyed the discussion.  

ਵਾਹਿਗੁਰੂ ਜੀ ਕਾ ਖਾਲਸਾ ਵਾਹਿਗੁਰੂ ਜੀ ਕੀ ਫਤਹਿ

To be continued

00 Part 4 Main PIC