A tithi runs between about 19 and 26 hours, and a day is about 24. So now and then a tithi begins after one sunrise and ends before the next. It holds no sunrise: a kshaya tithi. Now and then one holds two sunrises: a vriddhi tithi. Each festival's rule says which day it takes then. For the date itself, the printed almanac of your tradition decides. A book's rule explains a date; it does not overrule the almanac.
☕ The Moon does not keep clock time
A tithi ends when the Moon has gained 12° on the Sun. The Moon's speed changes through its orbit, so a tithi can be several hours shorter or longer than a day.
The almanac names each day by the tithi at sunrise. A short tithi that begins after sunrise and ends before the next sunrise is never at a sunrise. It is kshaya, lost. The day after it is named by the next tithi, so a number is skipped.
A long tithi can stand at two sunrises in a row. It is vriddhi, grown, and two days carry the same tithi.
A festival on a kshaya tithi cannot use the plain sunrise rule. It needs a fallback: often the day the tithi begins, sometimes the day it ends. A festival on a vriddhi tithi has two candidates and must pick one.
Kshaya also has a narrower meaning. Nirnaya Sindhu reads a verse about a Chaturdashi “in kshaya” as one that ends before the bath-time, not one that misses sunrise (Nirnaya Sindhu of Kamalakara Bhatta, p. 148). The word's sense depends on the rite.
At a glance
- Navaratri: a 1982 note in the Ahobila Mutt's almanac counts so that Navami is the ninth day: with a vriddhi tithi in the nine, a Dvitiya start; with a kshaya one, an Amavasai start. Its 2026-27 almanac starts on the Prathamai.
- Vijayadashami: when Dasami holds no sunrise, the almanac keeps it on the day that Dasami ends.
- A kshaya Ekadashi: the almanac keeps the vratam on the Dwadashi day.
- Sri Rama Navami: when the Ashtami test has moved the festival to the next day, it stays there even if Navami ended before that sunrise, on the Dasami (Ahnika Grantham, Vol. 1 (Sri Ahobila Mutt), pp. 330–333).
- What Nava does: Navaratri Utsava Arambham is kept on the day a kshaya Prathamai begins, and on the first of a vriddhi Prathamai's two sunrises. Vijayadashami, when Dasami holds no sunrise, is kept on the day after Mahanavami, the day it ends. A kshaya Ekadashi's fast is kept on the Dwadashi day by both traditions. A vriddhi Ekadashi's Smartha Ekadashi is the second of its two days.
Frequently asked questions
Why is a tithi number sometimes missing from the almanac?
That tithi began after one sunrise and ended before the next, so no day was named by it. It is a kshaya tithi. It still happened; it just held no sunrise.
Why do two days in a row show the same tithi?
The tithi was long enough to stand at both sunrises. It is a vriddhi tithi. A festival on it has two candidate days, and its rule picks one.
Can a festival vanish in a year because of a kshaya tithi?
A rule that only asks for the tithi at sunrise would find no day. That is why festival rules carry a fallback for the kshaya case, such as the day the tithi begins.
Deep dive: a kshaya tithi on a timeline
Three tithis across two sunrises, and the day each festival rule would pick.
📆 Three tithis, two sunrises
Monday's sunrise has Navami. Navami ends at 08:00 Monday. Dasami runs from 08:00 Monday to 05:30 Tuesday. Tuesday's sunrise, at 06:10, has Ekadashi.
Dasami held no sunrise: it is kshaya. A rule that takes the day the tithi begins picks Monday. A rule that takes the day it ends picks Tuesday. Both readings are found in the almanacs, festival by festival.
🔗 Read first
This page builds on which time of day a festival checks.