Tithis and Festivals: How Hindu Dates Are Set

Most Hindu festivals are fixed not by the solar calendar but by the tithi, the lunar day. That is why Diwali, Holi and Ganesh Chaturthi fall on different Gregorian dates each year, and why a festival can sometimes be observed on different days in different cities.

The lunar month

A lunar month has thirty tithis. Each is the time the Moon takes to gain 12 degrees on the Sun. The first fifteen, from new moon to full moon, form Shukla Paksha, the bright fortnight, ending at Purnima. The next fifteen form Krishna Paksha, the dark fortnight, ending at Amavasya. India uses two ways of naming months: in the amanta system, used in most of South and Western India, a month ends at new moon; in the purnimanta system of North India it ends at full moon. The same Krishna Paksha day can therefore belong to differently named months in Gujarat and in Uttar Pradesh, though the festival itself falls on the same day.

The sunrise rule

The tithi in force at local sunrise, the udaya tithi, is the tithi of the whole day for most purposes. Because tithis vary from about 19 to 26 hours, one sometimes begins after one sunrise and ends before the next; it never touches a sunrise and is called kshaya, a lost tithi. Another can span two sunrises and is counted twice, adhika. Sunrise differs from place to place, so the same tithi can be the udaya tithi on different days in Kolkata and in Mumbai — the source of many “which day is the festival?” questions.

Exceptions to the sunrise rule

Some observances depend on the tithi at another time of day. Diwali’s Lakshmi Puja needs Amavasya during Pradosh, the period after sunset. Janmashtami looks for Ashtami at midnight, the hour of Krishna’s birth. Ganesh Chaturthi prefers Chaturthi at midday. Mahashivaratri needs Chaturdashi at night. Ekadashi has its own rule: if Dashami is still running at Arunodaya, about an hour and a half before sunrise, Vaishnava traditions move the fast to the next day.

Important tithis

• Ekadashi (11th of each fortnight): a fast day dedicated to Vishnu, 24 in a year.
• Pradosh (13th): evening worship of Shiva.
• Chaturthi (4th): Ganesha; Sankashti Chaturthi in the dark fortnight.
• Purnima (full moon): Satyanarayan puja, Guru Purnima, Raksha Bandhan, Holi.
• Amavasya (new moon): rites for ancestors; Diwali in Kartika.
• Navami (9th): Rama Navami, and the ninth day of Navaratri.

The extra month

Twelve lunar months are about eleven days shorter than a solar year. To keep festivals in their seasons, an extra month, Adhika Masa or Purushottam Masa, is inserted roughly every 32 to 33 months, when two new moons fall while the Sun is in the same sign. Weddings and other ceremonies are usually avoided in it, but it is valued for devotion.

Solar festivals

A few festivals follow the Sun instead. Makar Sankranti marks the Sun entering sidereal Capricorn, around 14 January, and the Tamil, Bengali and Odia new years, with Kerala’s Vishu, are set by the Sun’s entry into Aries in mid-April. These move far less from year to year.

Our Panchang and festival pages calculate tithis for your own city, so the date you see is the one that applies where you live.