What is a Tithi?

A tithi is the lunar day: the time in which the Moon gains exactly twelve degrees on the Sun. Thirty tithis make up a lunar month, fifteen in the waxing Shukla Paksha and fifteen in the waning Krishna Paksha. Because the Moon’s speed varies, a tithi lasts between roughly 21 and 26 hours — it never fits neatly inside a calendar day.

The thirty names

Each paksha uses the same fifteen names: Pratipada, Dwitiya, Tritiya, Chaturthi, Panchami, Shashthi, Saptami, Ashtami, Navami, Dashami, Ekadashi, Dwadashi, Trayodashi, Chaturdashi, and finally Purnima (full moon) in the bright half or Amavasya (new moon) in the dark half.

Tithi at sunrise, not midnight

Because the Hindu day starts at sunrise, the tithi of a date is the one current at sunrise. Festivals and vrats are dated by this rule, with anchor refinements for some observances — for example Pradosh is dated by the tithi at sunset, and Karwa Chauth by the tithi at moonrise.

When a tithi skips every sunrise (kshaya)

A short tithi can begin after one sunrise and end before the next, touching no sunrise at all. This is a kshaya. Smarta convention dates such an observance to the day the tithi begins; Vaishnava tradition moves it to the next day. Our Ekadashi pages state both when it applies.

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