Indian national calendar
The Indian National Calendar (also Saka Calendar) is the official civil calendar in use in India. It is used, alongside the Gregorian Calendar, by the Gazette of India, news broadcasts by All India Radio, and calendars and communications issued by the Government of India.
It may also ambiguously refer to the Hindu Calendar.
Calendar structure
| Month | Length | Start date (Gregorian) | |
| 1 | Chaitra | 30/31 | March 22* |
| 2 | Vaisakha | 31 | April 21 |
| 3 | Jyaistha | 31 | May 22 |
| 4 | Asadha | 31 | June 22 |
| 5 | Sravana | 31 | July 23 |
| 6 | Bhadra | 31 | August 23 |
| 7 | Asvina | 30 | September 23 |
| 8 | Kartika | 30 | October 23 |
| 9 | Agrahayana | 30 | November 22 |
| 10 | Pausa | 30 | December 22 |
| 11 | Magha | 30 | January 21 |
| 12 | Phalguna | 30 | February 20 |
In leap years, Chaitra has 31 days and starts on March 21 instead. Like the Persian calendar, the months in the first half of the year all have 31 days, to take into account the slower movement of the sun across the ecliptic at this time.
The names of the months are derived from older, Hindu lunisolar calendars, so variations in spelling exist, and there is a possible source of confusion as to what calendar a date belongs to.
Years are counted in the Saka Era, which starts its year 0 in 78. To determine leap years, add 78 to the Saka year - if the result is a leap year in the Gregorian calendar, then the Saka year is a leap year as well.
Adoption
The calendar was introduced by the Calendar Reform Committee in 1957, as part of the Indian Ephemeris and Nautical Almanac, which also contained other astronomical data, as well as timings and formulae for preparing Hindu religious calendars, in an attempt to harmonize this practice. Despite this effort, local variations based on older sources such as the Surya Siddhanta may still exist.
Usage officially started at Chaitra 1, 1879 Saka Era, or March 22 1957. However, government officials seem to largely ignore the New Year's Day of this calendar in favour of the religious calendar [1].