In one paragraph
A tithi is a lunar day: the time it takes the Moon to gain 12° on the Sun. Thirty tithis make one lunar month — fifteen in the waxing fortnight (Shukla Paksha), ending at the full moon, and fifteen in the waning fortnight (Krishna Paksha), ending at the new moon. Because the Moon's speed varies, a tithi lasts anywhere from about 19 to about 26 hours and does not start or end at any fixed time of day.
How a tithi is measured
At the new moon the Sun and Moon sit at the same point of the zodiac. The Moon then pulls ahead. Each time the gap between them grows by another 12°, one tithi ends and the next begins. After fifteen such steps the gap is 180° — the full moon. After thirty it is 360°, the Moon has caught the Sun again, and the month is over.
The calculation is simply the Moon's longitude minus the Sun's longitude, divided by twelve. It involves only the two luminaries, which is why the tithi is the same everywhere on Earth at any given instant — only the local clock time at which it changes differs.
The fifteen tithis
| # | Tithi | Group |
|---|---|---|
| 1 | Pratipada | Nanda |
| 2 | Dwitiya | Bhadra |
| 3 | Tritiya | Jaya |
| 4 | Chaturthi | Rikta |
| 5 | Panchami | Purna |
| 6 | Shashthi | Nanda |
| 7 | Saptami | Bhadra |
| 8 | Ashtami | Jaya |
| 9 | Navami | Rikta |
| 10 | Dashami | Purna |
| 11 | Ekadashi | Nanda |
| 12 | Dwadashi | Bhadra |
| 13 | Trayodashi | Jaya |
| 14 | Chaturdashi | Rikta |
| 15 | Purnima (bright half) / Amavasya (dark half) | Purna |
Why a tithi is not 24 hours long
The Moon's orbit is an ellipse. Near its closest point to the Earth the Moon moves fast and covers 12° of separation quickly; near its farthest point it moves slowly. A lunar month of about 29.5 days divided into 30 tithis gives an average of about 23 hours 37 minutes each, but individual tithis range from roughly 19 hours to roughly 26.
This is why a tithi can end at four in the morning one day and at two in the afternoon on another. Any almanac that prints a single tithi for a date is quietly applying a rule to decide which one counts.
The sunrise rule, skipped and repeated tithis
For most purposes, the tithi in force at sunrise names the whole day. This is the udaya tithi rule, and it is what Astronaad's Panchang uses.
Two consequences follow. A short tithi can begin just after one sunrise and end before the next — so it is never in force at any sunrise and is "lost" (kshaya). A long tithi can be in force at two consecutive sunrises, and is then counted twice (vriddhi). Neither is an error; both are the calendar staying honest to the Moon.
Festivals are not always decided at sunrise. Many are fixed by the tithi prevailing at a particular time of day — midday for Ram Navami and Ganesh Chaturthi, the afternoon for Dussehra, the evening for Diwali. That is why a festival date occasionally differs by a day between two almanacs calculated for different places.
The five groups
The tithis fall into five groups that repeat in order, shown in the third column of the table:
- Nanda (1st, 6th, 11th): joyful — celebrations and enjoyment
- Bhadra (2nd, 7th, 12th): sound — beginnings and steady work
- Jaya (3rd, 8th, 13th): victorious — contests and overcoming obstacles
- Rikta (4th, 9th, 14th): "empty" — traditionally avoided for auspicious beginnings
- Purna (5th, 10th, 15th): full — completion and fulfilment
Muhurat selection leans on this. The Rikta tithis — Chaturthi, Navami and Chaturdashi — are usually excluded when choosing a date for a wedding, housewarming or new venture.
Tithis you will meet most often
- Ekadashi (11th): a fasting day in both fortnights — about 24 in a year
- Chaturthi (4th): sacred to Ganesha — Vinayaka Chaturthi in the bright half, Sankashti in the dark half
- Trayodashi (13th): the Pradosh observance for Shiva at twilight
- Purnima (15th, bright half): the full moon, a day of worship and many festivals
- Amavasya (15th, dark half): the new moon, kept for remembering ancestors
Frequently asked questions
- What is a tithi in simple terms?
- A lunar day. It is the time the Moon takes to move 12° further ahead of the Sun. There are thirty in a lunar month: fifteen while the Moon waxes and fifteen while it wanes.
- How long does a tithi last?
- On average about 23 hours 37 minutes, but it varies from roughly 19 to roughly 26 hours because the Moon speeds up and slows down along its elliptical orbit.
- What is the difference between Shukla Paksha and Krishna Paksha?
- Shukla Paksha is the bright, waxing fortnight from the new moon to the full moon. Krishna Paksha is the dark, waning fortnight from the full moon back to the new moon. The same tithi names occur in both.
- Why does a tithi sometimes get skipped?
- A day takes its tithi from the one in force at sunrise. A short tithi can start after one sunrise and finish before the next, so no day is named after it. It still occurred — it simply did not touch a sunrise.
- Which tithis are considered inauspicious?
- The Rikta tithis — the 4th, 9th and 14th of either fortnight — are traditionally avoided for starting important work, as is Amavasya for most celebrations. They remain appropriate for their own observances.
Work it out for yourself
These tools compute what this guide explains, from real astronomical positions.
- Panchang →Today's tithi and the exact time it ends, for your city.
- Amavasya Dates →Every new-moon date for the year.
- Purnima Dates →Every full-moon date for the year.
How this guide was written
The reference tables on this page are generated from the same data Astronaad’s calculators run on, so the guide and the tools cannot disagree. Where classical authorities differ, the text says so and names the convention Astronaad follows. Astrology is a traditional system of interpretation: nothing here is medical, legal or financial advice. Spotted an error? Tell us.