The Saka era, also known as the Shalivahana Saka era was adopted by the Indian government as the Indian national calendar. Its year zero begins near the vernal equinox of the year 78. Saka Calendar begins on 22 March every year except in leap years when it starts on 23 March. The Kushana emperor Kanishka is credited with the initiation of the Saka era on his accession to the throne in 78 A D. After the downfall of Kushanas their feudatory, the Sakas of Ujjain continued to use this era. Astronomer like Varahmihir, mathematician Brahmgupta and historian like Kalhana used Saka era in their celebrated works. Gurjaras of Bhinmal, Chalukyas of Badami and Rastrkutas of Deccan used the Saka era. In fact Saka era was most widespread over a span of historical times in India and it was one of the main reason for the 'Calendar Reform Committee' decided for Saka era to be the Indian National Calendar.
Shak calendar is a solar calendar having fixed number of days in each month. The other popular era in India and some of the adjacent countries is Vikram Samwat (विक्रम संवत). The Vikram Samwat follows a calculation of time by observing a complex fusion of lunar and solar calendars. However the names of months in both the calendar are same. Saka calendar start with Chaitra (चैत्र) followed by Vaisakh (वैसाख), Jyestha (ज्येष्ठ), Ashadh (अषाढ़), Shravan (श्रावण), Bhadrapad (भाद्रपद), Ashwin (आश्विन), Kartik (कार्तिक), Margshish (मार्गशीष), Paush (पौष), Magh (माघ) and Falgun (फाल्गुन) whereas Vikram calendar starts with Kartik as first month of the year.
Some tales in India state that the Saka era started at 78 A.D. to celebrate victory of Gautamiputra Satakarni over western satraps, known as Sakas. The 1st day of Saka Calendar is celebrated as new year in areas of Maharashtra and Goa as Gudi Padwa, in Karnataka, Andhra Pradesh and Telangana as Ugadi.
The era was also used by Javanese courts from Old Javanese times until 1633, when it was replaced by Anno Javanico, a hybrid Javanese-Islamic system.(pp5 and 46)It is also this particular era which aided historians in dating the Laguna Copperplate Inscription, the earliest written document found in the Philippines.
It has been used not only in many Indian inscriptions but also in ancient Sanskrit inscriptions in Southeast Asia. The reformed calendar promulgated by the Indian government from 1957 is reckoned by this era.