A tithi is a lunar day. Each tithi is the time it takes the Moon to move 12 degrees further away from the Sun. Because the Moon's speed varies, a tithi can last anywhere from about 19 to 26 hours, and it can begin or end at any time of day.
A lunar month has 30 tithis, split into two halves (paksha) of 15.
Shukla and Krishna paksha
- Shukla paksha (bright half): from new moon to full moon, as the Moon waxes. Traditionally better for starting things.
- Krishna paksha (dark half): from full moon to new moon, as the Moon wanes. A time for completing, clearing and reflection.
The 15 tithis of each paksha
- Pratipada
- Dwitiya
- Tritiya
- Chaturthi
- Panchami
- Shashthi
- Saptami
- Ashtami
- Navami
- Dashami
- Ekadashi
- Dwadashi
- Trayodashi
- Chaturdashi
- Purnima (in Shukla paksha) or Amavasya (in Krishna paksha)
The five tithi groups
| Group | Tithis | Nature |
|---|---|---|
| Nanda | 1, 6, 11 | Joyful: celebrations, arts, new clothes |
| Bhadra | 2, 7, 12 | Steady: practical and health-related work |
| Jaya | 3, 8, 13 | Victory: competitions, decisive action |
| Rikta | 4, 9, 14 | Empty: avoided for new beginnings |
| Purna | 5, 10, 15 | Complete: good for most auspicious work |
Amavasya is reserved for honouring ancestors and is avoided for new beginnings.
Important tithis
- Ekadashi (11th): fasting day for Vishnu devotees, twice a month.
- Pradosh (Trayodashi, 13th): evening worship of Shiva.
- Sankashti Chaturthi (4th of Krishna paksha): Ganesha fast, broken at moonrise.
- Purnima: full moon, good for worship and charity.
Why a tithi can be "skipped" or repeated
Because tithis do not line up with sunrise, occasionally one tithi starts after one sunrise and ends before the next, so it is never "the tithi at sunrise" and seems to be skipped (kshaya tithi). Sometimes a tithi spans two sunrises and appears twice (adhika tithi). This is why festival dates sometimes need care.
Tithi and the Moon's phase
You can roughly see the tithi in the sky. Around Shukla Ashtami (the 8th) the Moon is a half disc in the evening sky; on Purnima it is full and rises at sunset; on Krishna Ashtami it is a half disc rising around midnight; on Amavasya it cannot be seen.