What Is a Tithi? How the Hindu Lunar Day Is Calculated
A tithi is the time the Moon takes to gain 12° on the Sun. Learn how tithis are calculated, why they vary in length, and how they shape every Hindu festival.
Ask anyone planning a puja, a griha pravesh or a fast, and the first question is always the same: which tithi is it? The tithi is the heartbeat of the Hindu calendar. Festivals, vrats, shraddha and muhurat all depend on it. Yet few people know what a tithi actually measures, or why it so often changes in the middle of the day.
The short answer
A tithi is a lunar day. It is the time it takes for the Moon to move 12 degrees ahead of the Sun in the sky, as seen from Earth.
At the new moon (Amavasya), the Sun and Moon share the same longitude. Every day the faster-moving Moon pulls ahead. When it is 12° ahead, the first tithi (Shukla Pratipada) ends. At 24° the second tithi ends, and so on. After 180° we reach the full moon (Purnima), and after 360° the Moon has caught up with the Sun again, completing the lunar month.
Since 360 ÷ 12 = 30, there are 30 tithis in every lunar month.
Shukla and Krishna Paksha
The 30 tithis are split into two fortnights, called paksha:
| Paksha | Moon | Tithis | Ends with |
|---|---|---|---|
| Shukla Paksha (bright half) | Waxing | Pratipada to Chaturdashi, then Purnima | Full moon |
| Krishna Paksha (dark half) | Waning | Pratipada to Chaturdashi, then Amavasya | New moon |
So "Krishna Ekadashi" means the eleventh tithi of the waning fortnight, when the Moon is between 300° and 312° ahead of the Sun.
Why tithis are not 24 hours long
A tithi is defined by an angle, not by the clock. The Moon's orbit is elliptical, so its speed changes. Near perigee (closest to Earth) it can travel more than 15° a day; near apogee it slows to under 12°. The Sun's apparent speed also varies slightly through the year.
As a result, a tithi lasts anywhere from about 19 hours 59 minutes to 26 hours 47 minutes. That simple fact explains most of the confusion around Hindu dates:
- A tithi can begin at any moment, such as 3:47 in the afternoon.
- A single civil day often contains two tithis.
- Occasionally a short tithi begins and ends between two sunrises and is "lost" from the calendar (kshaya tithi).
- A long tithi can cover two sunrises and appear on two consecutive days (vriddhi tithi).
We explain those cases in detail in Why are there two tithis in one day?
The tithi of the day: udaya tithi
For most purposes, the tithi that prevails at sunrise is the tithi of the whole day. This is called the udaya tithi. If Dashami is running at sunrise and Ekadashi begins at 10 a.m., the day is still counted as Dashami in the calendar.
Sunrise depends on where you are, which is why the tithi of a day can differ between Mumbai and Kolkata, and very often between India and the USA. Always check the panchang for your own city.
Some observances follow a different moment. Pradosh Vrat needs Trayodashi at sunset, Sankashti Chaturthi needs Chaturthi at moonrise, and Maha Shivaratri needs Chaturdashi at midnight. Read more in our guide to udaya tithi and observance rules.
Is the tithi the same everywhere?
Yes and no. The instant a tithi begins is the same for the whole world, because it depends only on the positions of the Sun and Moon. But local clocks differ. A tithi that begins at 11:30 p.m. in New Delhi begins at 1:00 p.m. the same day in New York. Combined with different sunrise times, the date on which a festival falls can genuinely differ between countries.
The five groups of tithis
Tradition groups the tithis of each paksha into a repeating cycle of five qualities:
- Nanda (joyful): Pratipada, Shashthi, Ekadashi
- Bhadra (auspicious): Dwitiya, Saptami, Dwadashi
- Jaya (victorious): Tritiya, Ashtami, Trayodashi
- Rikta (empty): Chaturthi, Navami, Chaturdashi
- Purna (complete): Panchami, Dashami, Purnima or Amavasya
The deities linked with tithis, such as Ganesha on Chaturthi and Vishnu on Ekadashi, are described in depth in SpiritualMarg's guide to Hindu deities.
Rikta tithis are usually avoided for beginnings such as weddings and house-warmings, while Nanda, Bhadra and Purna tithis are preferred. Each tithi also has a presiding deity; see the complete tithi guide for all thirty.
How we calculate tithi
On this site, the Sun's and Moon's apparent positions are computed with modern ephemeris algorithms, and the exact second each 12° boundary is crossed is found numerically. That is the same approach used by leading digital panchangs, so you can rely on the start and end times you see on today's tithi.
Key takeaways
- A tithi is 12° of Moon–Sun separation; there are 30 in a lunar month.
- Tithis vary from about 20 to 27 hours, so they start at all hours.
- The tithi at local sunrise is the tithi of the day for most rituals.
- Location matters, so always use a panchang calculated for your city.