Why Does One Tithi Last Two Days? Tithi Kshaya and Vriddhi, Explained with Navratri 2026
A tithi is the Moon gaining 12 degrees on the Sun. It runs about 19 to 26 hours, so it does not fit the clock day: sometimes one tithi is present at two sunrises (vriddhi), sometimes at none (kshaya). Navratri 2026's Saptami falls on both 17 and 18 October.
A tithi is not a 24-hour day. It is set by the Moon's motion and runs roughly 19 to 26 hours, averaging 23 hours 37 minutes. So sometimes one tithi is still running at two consecutive sunrises and is counted on two dates: that is tithi vriddhi (an "extended" tithi). And sometimes a tithi touches no sunrise at all and gets no date: tithi kshaya (a "dropped" tithi). In Navratri 2026, Saptami falls on both 17 and 18 October. That is vriddhi.
What is a tithi, and why doesn't it match the calendar date?
A calendar date runs by the clock: midnight to midnight, exactly 24 hours. A tithi runs by the sky. One tithi is complete when the Moon has moved 12 degrees ahead of the Sun.
The Moon does not travel at a constant speed. So covering those 12 degrees takes it anywhere from about 19 hours to about 26. A tithi can therefore begin or end at any hour: 05:54 in the morning, 12:50 in the afternoon, whenever the sky says so.
So which tithi does a date "get"? The rule is simple: the tithi running at sunrise is the tithi of that whole day. This is called the udaya tithi (udaya = sunrise). The basic difference between a tithi and a calendar date is covered in Tithi vs English date: what is the difference.
Why is one tithi counted on two days? (Tithi vriddhi)
When a tithi is longer than 24 hours and begins a little before sunrise, it is still running at the next sunrise too. Both days get the same tithi. That is tithi vriddhi: the tithi has "grown".
Saptami (the 7th tithi) of Navratri 2026 is a clean example. Shukla means the bright, waxing fortnight. The Delhi numbers:
- Shukla Saptami begins: 17 October, 05:54
- Sunrise on 17 October: 06:24 — Saptami is running
- Sunrise on 18 October: 06:24 — Saptami is still running
- Saptami ends: 18 October, 08:28
Saptami started only 30 minutes before sunrise and lasted over 26 hours, two hours past the next sunrise. Both mornings belong to it. That is why our panchang labels both 17 October (Saturday) and 18 October (Sunday) as "Shardiya Navratri — Day 7". It is not an error; Saptami genuinely runs for two days this year.
And why does a tithi sometimes vanish from the calendar? (Tithi kshaya)
The reverse also happens. When a tithi is shorter than 24 hours, begins after sunrise and ends before the next sunrise, it touches no morning at all. It gets no date. That is tithi kshaya: the tithi has "shrunk". The panchang then shows two tithi names against one date, and people ask how one day can hold two tithis.
In 2026 the effect shows up in two places.
Navratri 2026: why Ashtami and Navami share a day, with Dussehra the next
After Saptami's vriddhi, the tithis run like this (Delhi):
- Shukla Ashtami (8th tithi): 18 October 08:28 to 19 October 10:52. Ashtami at sunrise (06:25) on 19 October.
- Shukla Navami (9th tithi): 19 October 10:52 to 20 October 12:50. Navami at sunrise (06:25) on 20 October.
- Shukla Dashami (10th tithi): begins 20 October at 12:50.
By udaya tithi alone, 19 October is Ashtami's day and 20 October is Navami's. So why does our panchang label 19 October "Durga Ashtami · Maha Navami" and 20 October "Vijayadashami" (Dussehra)?
Because festivals do not look only at sunrise. They look at which tithi is running at the time of the ritual. Dussehra's time, by tradition, is aparahna, the later part of the afternoon. On 20 October, Dashami arrives at 12:50, so Dashami holds the afternoon, and Vijayadashami is 20 October. Maha Navami puja is done from midday (madhyahna) onward; on 19 October, Navami is running from 10:52, so Navami puja is on the 19th. And the morning of the 19th is Ashtami, so Durga Ashtami is also the 19th.
Strictly speaking, this is not a tithi kshaya: Navami does touch the sunrise of 20 October. But in the festival count, Navami does not get a separate day of its own, and the effect on the calendar looks the same: two observances on one date. The full nine-day sequence is in the Navratri 2026 complete 9-day calendar.
Dev Uthani Ekadashi 2026: when a tithi begins after sunrise
The second example is in November. In Delhi, sunrise on 20 November is at 06:48, and Dashami is running at that moment (Dashami: 19 November 07:05 to 20 November 07:14). Ekadashi (the 11th tithi) begins at 07:14, 26 minutes after sunrise.
By udaya tithi, 20 November is a Dashami day. Yet the Dev Uthani Ekadashi fast is on 20 November, because the whole afternoon and evening of that day pass in Ekadashi. This is exactly the setup from which a tithi kshaya arises: the tithi narrowly misses the morning. The full working, and how it opens the wedding season, is in our Dev Uthani Ekadashi 2026 post.
Four rules that decide the date of a vrat or festival
In tradition, every observance has a "time of day", and its date is fixed by the tithi running at that time. Four rules cover most cases:
- Fasts (vrat) — udaya tithi. Most fasts are kept on the day whose sunrise falls within that tithi.
- Evening festivals — pradosh tithi. Pradosh is the period after sunset. Diwali, Dhanteras and Pradosh vrat are dated by whichever tithi is running that evening.
- Midnight observances — nishita tithi. Nishita is midnight. Janmashtami and Shivratri are dated by the tithi at midnight.
- Afternoon observances — aparahna tithi. Dussehra and the Bhai Dooj tilak are dated by the tithi in the later afternoon.
Apply these to the example above: the udaya tithi of 20 October is Navami, yet Dussehra is that day, because Dashami holds the afternoon. Different rule, different date, both correct.
Six real days of 2026: which tithi was at sunrise?
These figures come from our panchang engine, for Delhi. In another city sunrise shifts by a few minutes, so in borderline cases the udaya tithi can change.
| Date (Delhi) | Sunrise | Tithi at sunrise | Tithi window | What the panchang shows |
|---|---|---|---|---|
| 17 October, Saturday | 06:24 | Shukla Saptami | 17 Oct 05:54 → 18 Oct 08:28 | Shardiya Navratri — Day 7 |
| 18 October, Sunday | 06:24 | Shukla Saptami | 17 Oct 05:54 → 18 Oct 08:28 | Shardiya Navratri — Day 7 (tithi vriddhi) |
| 19 October, Monday | 06:25 | Shukla Ashtami | 18 Oct 08:28 → 19 Oct 10:52 | Durga Ashtami · Maha Navami (Navami from 10:52) |
| 20 October, Tuesday | 06:25 | Shukla Navami | 19 Oct 10:52 → 20 Oct 12:50 | Vijayadashami (Dashami from 12:50, aparahna rule) |
| 19 November, Thursday | 06:47 | Shukla Navami | 18 Nov 06:04 → 19 Nov 07:05 | Navami ends 18 minutes after sunrise, yet the day is Navami's |
| 20 November, Friday | 06:48 | Shukla Dashami | 19 Nov 07:05 → 20 Nov 07:14 | Dev Uthani Ekadashi (Ekadashi from 07:14) |
Why do two panchangs give different dates for the same festival?
The answer is now clear. One panchang took the udaya tithi; the other took the tithi at the ritual's time. Both are honest. The difference is in the rule, not the arithmetic.
The second reason is place. Sunrise differs by a few minutes from city to city. When a tithi is changing right around sunrise, as on 20 November with only a 26-minute gap, a city with a later sunrise can end up with a different udaya tithi. That is why every figure we publish comes with its city.
How to check the tithi for your own city
Look at three things:
- The sunrise time in your city that day.
- When the tithi begins and when it ends.
- Which part of the day your puja belongs to: morning, evening, midnight or afternoon.
Combine the first two and you have the udaya tithi. Add the third and the festival date follows. Our daily panchang shows sunrise, the tithi window and the festival label together for every day; those three figures are all this article is built from.