Most Hindu festivals are fixed by a tithi, a lunar day, not by a date on the solar calendar. That is why Diwali can move by almost three weeks from one year to the next, and why two calendars sometimes print different dates for the same festival in the same year. Four things decide the date: the festival's deciding time of day, local sunrise, tithis that are skipped or repeated, and the tradition a calendar follows.
The examples below are from the 2026 season. Festival dates are taken from published panchangs. Tithi and sunrise times are AstroMystra's own calculation, in IST, and run within about two minutes of Drik Panchang's published times.
What a tithi is
A tithi is one-thirtieth of the cycle from new moon to new moon. Each tithi is a 12° step in how far the Moon is ahead of the Sun: Shukla Pratipada while the Moon is 0–12° ahead, Shukla Dwitiya at 12–24°, and so on to Purnima, then the Krishna Paksha tithis down to Amavasya. The Moon's speed varies, so a tithi lasts roughly 19 to 26 hours.
Two things follow from that definition:
- A tithi begins and ends at the same instant everywhere. India has one time zone, so the IST clock time of a tithi change is the same in every Indian city.
- Tithis do not line up with calendar days. A tithi can begin late one morning and end around midday the next.
1. The festival's deciding time of day
A tithi usually covers parts of two dates, so each festival has a rule for which moment counts. The festival pages on this site use these rules:
- Dhanteras and Diwali (Lakshmi Puja): the tithi must hold in Pradosh Kaal, the period after sunset.
- Karva Chauth: Krishna Chaturthi at moonrise.
- Chhath Puja: Shukla Shashthi at sunset, the time of Sandhya Arghya.
- Dussehra and Bhai Dooj: the tithi in the afternoon.
- Sharad Navratri: Shukla Pratipada in the morning, for Ghatasthapana.
Diwali 2026. Amavasya runs from 8 November, 11:28 to 9 November, 12:32. It touches both dates. On the evening of 8 November it holds through Pradosh Kaal; on 9 November it ends hours before sunset (17:31 in Delhi). Lakshmi Puja is therefore on 8 November, even though Amavasya is the tithi at sunrise on 9 November. A calendar that only lists each day's sunrise tithi can make 9 November look like Diwali. Diwali 2026 timings by city.
Karva Chauth 2026. Krishna Chaturthi runs from 29 October, 01:07 to 29 October, 22:11. Moonrise in Delhi is at 20:17, inside the tithi, so the fast is on 29 October. Because the rule checks moonrise, the time that matters is local: 19:46 in Kolkata, 20:17 in Delhi and 21:00 in Mumbai. Karva Chauth 2026 moonrise by city.
Chhath Puja 2026. Shukla Shashthi runs from 14 November, 23:25 to 16 November, 02:02, so it covers the whole of 15 November, sunset included. Sandhya Arghya is on 15 November and Usha Arghya on the morning of 16 November. Chhath Puja 2026 by city.
2. Local sunrise
A panchang names each day by the tithi in force at local sunrise. India spans about 29° of longitude, so sunrise in the east can come an hour or more before sunrise in the west, while the tithi changes at the same instant everywhere. When a tithi ends shortly after sunrise, two cities can list different tithis for the same date.
24 December 2026. Purnima ends at 06:58. Sunrise in Kolkata is at 06:13, inside Purnima, so a Kolkata panchang lists 24 December as Purnima. Sunrise in Ahmedabad is at 07:17, after Purnima has ended, so an Ahmedabad panchang lists Krishna Pratipada. Our calculation finds eight such dates for these two cities between 20 October 2026 and 31 March 2027.
The rules that check sunset or moonrise also depend on place, but for the major festivals they seldom change the date. For each of the seven festival pages here, the 2026 date holds the deciding tithi in all 30 cities the pages cover. You can see any city's sunrise tithi on today's panchang.
3. A skipped or repeated tithi
A tithi lasts 19 to 26 hours and a day about 24, so the two drift. Sometimes a tithi begins after one sunrise and ends before the next, so it is the sunrise tithi of no day at that place; this is a kshaya (skipped) tithi. At other times one tithi holds at two sunrises in a row (an adhika or vriddhi tithi). A festival tied to such a tithi needs a tie-break rule, and panchangs can differ on it.
Sharad Navratri 2027. On 30 September 2027 Amavasya is still in force at sunrise. Shukla Pratipada begins at about 08:05 and ends before the next sunrise, so it holds at no sunrise in Delhi. Panchangs still set Ghatasthapana on 30 September, in the morning window after Pratipada begins: 08:05–10:12 in Delhi according to Drik Panchang (our calculation gives 08:06–10:12).
4. Tradition and calendar
- Regional practice. Some communities follow a different rule for the same festival, or observe it a day apart. The festival pages note this; a family's or temple's own panchang settles it for them.
- Month names. In the Purnimanta calendar a month ends on the full moon; in Amanta it ends on the new moon. The same Diwali Amavasya is Kartik Amavasya in one and Ashvin Amavasya in the other, but the day is the same.
- Adhik Maas. Twelve lunar months are about 11 days shorter than the solar year, so festivals usually come about 11 days earlier each year. Every two to three years an extra month is added, and dates then move later. 2026 has an Adhik Maas, which is why its festivals fall later than 2025's.
- Calculation method. Modern panchangs compute the true positions of the Sun and Moon. Some traditional almanacs still use older methods, and their tithi times can differ from modern ones.
How to check a festival date yourself
- Find the festival's tithi and its deciding time of day.
- Look up when that tithi begins and ends. Each festival page shows this in IST.
- Check whether the deciding moment in your city, on the date in question, falls inside that span.
- If your family or temple follows a particular panchang, use its date.
References and scope
Tithi and the Hindu calendar on Wikipedia describe the 12° definition, the sunrise tithi, and skipped and repeated tithis. Drik Panchang's daily panchang publishes city-wise tithi times. Our methodology describes how this site calculates. This guide explains calculation rules, not religious practice.