What is Tithi?

A Tithi is a lunar day: the time it takes for the angular distance between the Moon and the Sun to increase by exactly 12°. Because the Moon moves at a varying speed in its orbit, a Tithi isn't a fixed 24 hours — it can run anywhere from about 19 to 26 hours. This is why, on rare occasions, a Tithi is skipped entirely within a solar day (Kshaya Tithi) or spans two solar days (Vriddhi Tithi).

30 tithis, two fortnights

A full lunar month has 30 tithis, split into two 15-day Pakshas (fortnights):

Shukla Paksha — the waxing fortnight, from Amavasya (new moon) to Purnima (full moon), when the Moon grows brighter each day.

Krishna Paksha — the waning fortnight, from Purnima back to Amavasya, when the Moon shrinks each day.

The 15 tithi names (Shukla Paksha)

The 15 tithi names (Krishna Paksha)

Why Tithi matters

Nearly every Hindu festival is fixed to a specific Tithi rather than a Gregorian date — Diwali falls on Krishna Paksha Amavasya of Kartik, Holi on Purnima of Phalgun, Ganesh Chaturthi on Shukla Paksha Chaturthi of Bhadrapada. See our Amavasya dates, Purnima dates and Ekadashi dates for 2026, or the full festival calendar. Want to know what Tithi it is right now? See our Today's Tithi page.