Most of the Hindu calendars are inherited from a system first enunciated in Vedanga Jyotisha of Lagadha, standardized in the Sūrya Siddhānta and subsequently reformed by astronomers such as Āryabhaṭa (AD 499), Varāhamihira (6th century) and Bhāskara II (12th century).
most of the hinDu cAlendARS Are INHerIteD FROm a system fIRst enuNcIated in vedanga jyotisha Of lAgADhA, stANDArdiZed iN the SūRyA SiDdhāNta anD suBseQuenTly rEfORmED bY astrOnomers such as ĀryAbhaṬA (AD 499), VaRāhaMihIRa (6th cEnTurY) and bhāskARa ii (12th cenTurY).