The udaya tithi rule

The rule in one line

Udaya = rising. The udaya tithi is the tithi that is running at sunrise. In the usual Panchang practice, that tithi is the tithi of the day, from that sunrise until the next sunrise, even if it ends a few minutes later.

This follows from the Hindu day itself, which runs from sunrise to sunrise. If the day is counted from sunrise, the tithi at that moment is the natural label for it.

An example in words

Suppose Shukla Dashami is running at sunrise on a Tuesday. It ends at midday, and Ekadashi begins. The Panchang calls Tuesday Dashami. Ekadashi is counted on Wednesday only if it is running at Wednesday's sunrise.

Now picture a tithi that begins at 7:00 a.m. after the sunrise and ends the next day at 6:00 a.m., before that day's sunrise. It was never running at any sunrise, so it has no day to itself. That is the kshaya, or lost, tithi. The reverse also happens. A tithi that is running at two sunrises in a row is counted on both days.

Why the site shows start and end times too

Tithis begin and end at any hour. A tithi can start in the evening and end the next afternoon. The site shows the exact start and end time of each tithi, nakshatra, yoga and karana in your local time. The udaya rule only tells you which tithi names the day. The times tell you when each one really changes.

This matters for rituals that must be done at a certain time of day, not just on a certain day.

Local sunrise makes a difference

Sunrise is different in every city. So the udaya tithi can differ between two cities on the same date. A tithi that ends at 6:40 a.m. in one city may still be running at sunrise in a city where the Sun rises earlier, and not in one where it rises later.

If you live in the USA, your tithi follows your own city's sunrise. A Panchang for an Indian city may name a different tithi for your date.

When festivals follow a different rule

The udaya rule is the default for naming days, but many festivals are decided by other rules.

• Some observances belong to a part of the day, such as the evening or midnight or moonrise. For these the tithi needed is the one present at that part of the day.
• Some fasts, such as Ekadashi, have extra rules about which day to keep when the tithi spans two sunrises or begins before sunrise. Smarta and Vaishnava traditions follow different conventions, and families may follow their own.
• Festivals with a fixed hour, such as Diwali puja in the evening, follow the tithi at that hour rather than at sunrise.

If a festival seems to be on a different day from the one you expected, check these rules first. The festival pages on this site say which day they use.

Not a mistake

Because a tithi is shorter than a day on average, tithi numbers move ahead of the weekday and the calendar sometimes appears to skip or repeat. This is normal and has been so for centuries. It is not an error in the Panchang.

If you are unsure which day to observe, follow your family's custom or ask your priest or temple.