Each year (called the Samvatsar, Shaka or Samvat), normally consists of the 12 months except when there is a Adhik Maas (Additional Month).Shaka Samvat
The Shalivahan Shaka Samvat is based on the lunar calendar and the new year starts with Chaitra Maas (Shukla Paksha). This calendar is believed to have been initiated by King Shalivahan in the year 78 A.D.
The Vikram Era started with Raja Vikramaditya of Ujjain, following his victory over the Saka in 56 B.C. The new year begins with the first day of Kartik following Deepawali Amaavasya.
The Yudhisthir Shaka, which started approximately around 5500 B.C, is not very popular today.