The Indian national calendar, sometimes called the Shalivahana Shaka calendar. It is used, alongside the Gregorian calendar, by The Gazette of India, in news broadcasts by All India Radio and in calendars and communications issued by the Government of India. The Saka calendar is also used in Java and Bali among Indonesian Hindus. Nyepi, the "Day of Silence", is a celebration of the Saka new year in Bali. Nepal's Nepal Sambat evolved from the Saka calendar. Prior to colonization, the Philippines used to apply the Saka calendar as well as suggested by the Laguna Copperplate Inscription.
The historic Shalivahana era calendar is still widely used. It has years that are solar.
The calendar months follow the signs of the tropical zodiac rather than the sidereal zodiac normally used with the Hindu calendar.
|#||Month (Sanskrit)||Length||Start date (Gregorian)||Tropical zodiac||Tropical zodiac (Sanskrit)|
Chaitra has 30 days and starts on March 22, except in leap years, when it has 31 days and starts on March 21. 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.
Years are counted in the Saka era, which starts its year 0 in the year 78 of the Common Era. 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. Its structure is just like the Persian calendar.
Senior Indian Astrophysicist Meghnad Saha was the head of the Calendar Reform Committee under the aegis of the Council of Scientific and Industrial Research. Other members of the Committee were: A. C. Banerjee, K. K. Daftari, J. S. Karandikar, Gorakh Prasad, R. V. Vaidya and N. C. Lahiri. It was Saha's effort, which led to the formation of the Committee. The task before the Committee was to prepare an accurate calendar based on scientific study, which could be adopted uniformly throughout India. It was a mammoth task. The Committee had to undertake a detailed study of thirty different calendars prevalent in different parts of the country. The task was further complicated by the integration of those calendars with religion and local sentiments. India's first prime minister, Jawaharlal Nehru, in his preface to the Report of the Committee, published in 1955, wrote: “They (different calendars) represent past political divisions in the country ... . Now that we have attained Independence, it is obviously desirable that there should be a certain uniformity in the calendar for our civic, social, and other purposes, and this should be done on a scientific approach to this problem.” 
Usage started officially at 1 Chaitra 1879, Saka Era, or 22 March 1957.
- Report of the Calendar Reform Committee (New Delhi: Council of Scientific and Industrial Research, 1955) – online link.
- Mapping Time: The Calendar and its History by E.G. Richards (ISBN 978-0-19-286205-1), 1998, pp. 184–185.
- Calendars and their History (by L.E. Doggett)
- Indian Calendars (by Leow Choon Lian, pdf, 1.22mb)
- Positional astronomy in India
- Indian National Calendar abstract