A tithi is not a day. It is the time the Moon takes to gain twelve degrees of separation from the Sun, and because both bodies move at varying speeds, that interval runs anywhere from about nineteen to about twenty-six hours. Thirty tithis of twelve degrees each complete the 360 degrees from one new moon to the next.
This is why a tithi does not line up with a calendar day, why it can begin in the middle of an afternoon, and why the Hindu calendar occasionally skips one or repeats one.
The definition
Take the Moon’s longitude, subtract the Sun’s, and normalise to a value between 0 and 360. Divide by 12. The result, rounded up, is the tithi number.
At new moon the separation is zero and the count begins. At full moon it is 180 degrees, which is exactly halfway — the fifteenth tithi. The cycle closes at 360, back at new moon.
The lunar month therefore divides cleanly in two. Shukla Paksha is the bright fortnight, tithis 1 to 15, from new moon to full. Krishna Paksha is the dark fortnight, tithis 1 to 15 again, from full moon back to new. A tithi is always named with its paksha, which is why a panchang reads “Krishna Navami” rather than “the twenty-fourth tithi”.
The thirty
| No. | Name | No. | Name |
|---|---|---|---|
| 1 | Pratipada | 9 | Navami |
| 2 | Dwitiya | 10 | Dashami |
| 3 | Tritiya | 11 | Ekadashi |
| 4 | Chaturthi | 12 | Dwadashi |
| 5 | Panchami | 13 | Trayodashi |
| 6 | Shashthi | 14 | Chaturdashi |
| 7 | Saptami | 15 (Shukla) | Purnima — full moon |
| 8 | Ashtami | 15 (Krishna) | Amavasya — new moon |
The names are simply the Sanskrit ordinals, first through fourteenth, with the fifteenth of each fortnight given its own name for the full and new moon.
The five groups, and why they matter for timing
The fourteen numbered tithis fall into five repeating groups of three, and this is the part that carries the practical weight in muhurta selection.
| Group | Tithis | Traditionally suited to |
|---|---|---|
| Nanda — joyful | 1, 6, 11 | Celebration, beginnings of a festive kind |
| Bhadra — auspicious | 2, 7, 12 | Construction, marriage, entering a house |
| Jaya — victorious | 3, 8, 13 | Contest, litigation, anything competitive |
| Rikta — empty | 4, 9, 14 | Avoided for auspicious work of any kind |
| Purna — full | 5, 10, 15 | Completion, travel, finishing what is started |
The Rikta group is the one worth committing to memory. The fourth, ninth and fourteenth tithis of either fortnight are traditionally avoided for marriage, for opening a business, for beginning construction and for setting out on a journey. This is one of the oldest and most consistently applied rules in the muhurta literature.
The exception, and it is a real one, is that Rikta tithis are considered suitable for exactly the things they are unsuitable for elsewhere — demolition, ending an arrangement, confronting an adversary. An empty tithi is good for emptying.
Kshaya and vriddhi: skipped and repeated tithis
Because a tithi runs between nineteen and twenty-six hours and a day runs twenty-four, the two drift against each other. The convention is that the tithi in force at sunrise names the day.
Two consequences follow. If a short tithi begins after one sunrise and ends before the next, no day carries its name — that is tithi kshaya, a skipped tithi. If a long tithi is in force at two consecutive sunrises, two days carry the same name — that is vriddhi or adhika, a repeated tithi.
This is not an error in the calendar. It is the calendar correctly reporting that lunar time and solar time do not divide evenly, and it happens several times a year. It is also why two panchangs computed for different longitudes can disagree about which tithi a given date carries: sunrise is local, so the tithi at sunrise is local too.
Where tithi sits in the panchang
Tithi is the first of the five limbs. The other four are nakshatra, the lunar mansion the Moon occupies; yoga, computed from the sum of the Sun’s and Moon’s longitudes; karana, which is half a tithi; and vara, the weekday. Reading a panchang means reading all five together.
Note that three of the five — tithi, nakshatra and yoga — are functions of the Sun and Moon positions alone. The panchang is very largely a description of the relationship between those two bodies, which is worth knowing when comparing it against a full chart reading that uses all nine.
Karana deserves a note of its own since it follows directly from tithi. Each tithi divides into two karanas of six degrees each, giving sixty karanas in a lunar month. Eleven karana names cycle through them, four of which are fixed and occur once per month around the new moon.
Common observances tied to tithi
Several of the most widely kept observances are defined by tithi rather than by date, which is why they move against the Gregorian calendar.
- Ekadashi, the eleventh tithi of each fortnight, is the most widely observed fasting day and occurs twice a lunar month.
- Chaturthi, the fourth, is associated with Ganesha, and the Krishna Paksha Chaturthi in particular with Sankashti.
- Ashtami and Navami, the eighth and ninth, carry a number of observances including those falling in Navaratri.
- Purnima and Amavasya anchor the fortnights, with Amavasya traditionally the day for rites for ancestors.
Common questions
How do I find today’s tithi?
Any panchang gives it, and the panchang page here computes it from the current Sun and Moon positions rather than looking it up. The arithmetic is one subtraction and one division if you have both longitudes.
Why do two sources give me different tithis for the same date?
Usually because the tithi changed during the day and the two sources use different conventions about which one names it, or because they are computed for different locations, so sunrise differs. Both can be correct for their own reference point.
Is the tithi at birth used in astrology?
Yes. Birth tithi is used in some compatibility methods and in certain classical yogas, and the paksha at birth — bright or dark fortnight — is itself a factor in some readings. It is a smaller input than the Moon’s nakshatra, which is what drives the dasha system.
Is Rikta tithi genuinely avoided?
In traditional practice, consistently. It is one of the first checks in muhurta selection and it is applied even by people who use very little else from the system. Whether one accepts the reasoning, it is not a modern invention.
The tithi calculation described here is arithmetic on the Sun and Moon longitudes and can be checked. The qualities assigned to each tithi group are the traditional attributions of the muhurta literature, not predictions about events.
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