India has as many new years as states. But there is a method to the madness.
The calendars can be grouped in five main variations. Two are solar, three are lunar.
The solar new years correspond to a specific day of the Gregorian Calendar, which is also solar. The lunar new years start on a specific phase of the moon.
The second solar group starts on the Sidereal Equinox, which adjusts for the wobble in the tilt of the earth. It starts around April 14. The calendars of Tamil Nadu, Kerala, Odisha, Assam (Bihu), West Bengal and Punjab (Baisakhi) are in this group. The equinox shifts away from the sidereal new year by about a day, every hundred years.
The first lunar group starts on the full moon following the equinox. This is Holi, celebrated as new year in Haryana, Bihar, Rajasthan, Madhya Pradesh, Uttarakhand, Jharkhand and Chhattisgarh.
The second lunar group starts on the new moon following the equinox. This is Ugadi in Karnataka, Andhra Pradesh, Telengana, Maharashtra and Konkan; Navreh in Kashmir and Vishu in Manipur.
And finally, Gujrat starts its calendar on Diwali, which falls on a new moon in autumn.