The Tamil calendar is a solar and sidereal Hindu calendar used in Tamil Nadu. It is also used in Pondicherry (India), and by the Tamil population in Malaysia, Singapore, Mauritius and Sri Lanka. It is also used by Telugu speaking people in Tamil Nadu. It is used today for cultural, religious and agricultural events, with the Gregorian calendar largely used for official purposes both within and outside India. The Tamil calendar is based on the classical Hindu solar calendar also used in Assam, Bengal, Kerala, Manipur, Nepal, Orissa, Rajasthan and the Punjab.

There are several festivals based on the Tamil Hindu calendar. The Tamil New Year follows the nirayanam vernal equinox and generally falls on 13 or 14 April of the Gregorian year. 13 or 14 April marks the first day of the traditional Tamil calendar and this remains a public holiday in both Tamil Nadu and Sri Lanka. Tropical vernal equinox fall around 22 March, and adding 23 degrees of trepidation or oscillation to it, we get the Hindu sidereal or Nirayana Mesha Sankranti (Sun's transition into nirayana Aries). Hence, the Tamil calendar begins on the same date in April which is observed by most traditional calendars of the rest of India - Assam, Bengal, Kerala, Orissa, Manipur, Punjab etc. This also coincides with the traditional new year in Burma, Cambodia, Laos, Sri Lanka, Bangladesh Nepal and Thailand. The 60-year cycle is also very ancient and is observed by most traditional calendars of India and China, and is related to 5 revolutions of Jupiter according to popular belief, or to 60-year orbit of Nakshatras (stars) as mentioned in Surya Siddhanta.