Why Your Festival Date Does Not Match India’s
How the Hindu calendar works, and how to find the right date for your own city

Your phone's calendar app says Diwali is on one date. Your mother says another. The temple newsletter says a third.

Nobody is lying, and nobody has made a mistake.

What has happened is that a calendar built on the sky is being read from three different places on the planet — and the sky does not care which timezone you are standing in. Once you understand that, you will never have to ask again. You will just look it up, in about two minutes, and know you are right.

The Hindu calendar runs on the moon, not the sun

Start here, because everything else follows from it.

The Gregorian calendar on your phone runs on the sun: 365 days, one trip around it, and the date changes at midnight whatever the sky is doing. The Hindu calendar is lunisolar — it counts months by the moon and years by the sun, and then reconciles the two.

That reconciliation is the interesting part:

“Twelve Hindu mas (māsa, lunar month) are equal to approximately 354 days, while the length of a sidereal (solar) year is about 365 days… This creates a difference of about eleven days, which is offset… approximately every 32.5 months.”

— the structure of the Hindu calendar

Eleven days a year of drift, corrected by inserting a whole extra month — Adhika Masa — roughly every third year. (This is why Diwali can fall in October one year and November the next. It is not random; it is the correction working.)

So a Hindu festival does not have a fixed Gregorian date, in the same way that Easter does not. It has a fixed position in a lunar month, and that position lands wherever the moon puts it.

Which brings us to the unit everything is actually measured in.

What a tithi is, in one paragraph

A tithi is the lunar day. It is not a day.

“A tithi is defined as the time taken for the longitudinal angle between the Sun and the Moon to increase by 12°… There are 30 tithis in each lunar month… The average tithi lasts 23 hours 37.5 minutes, and can range from 19 hours 59 minutes to 26 hours 47 minutes.”

— the definition of a tithi

Read that last clause again, because it is the whole article in one line: a tithi can be as short as 20 hours or as long as 27. It is not 24. It does not start at midnight. It starts and ends at whatever clock time the moon's geometry reaches the next 12° mark.

Which means a tithi does not fit neatly inside a calendar date. It leaks. It can begin on Tuesday afternoon and end on Wednesday evening. And two things follow from that, which have names:

• Kshaya tithi — a tithi that begins after one sunrise and ends before the next, so it never touches a sunrise at all.
• Adhika tithi — a tithi still running at two consecutive sunrises, so it covers two days.

(Neither is a bad omen. They are arithmetic.)

Why the same tithi lands on different dates in different countries

Here is the thing people get backwards.

The tithi itself is identical everywhere. It is a fact about the angle between two objects in space, so it begins at one single instant for the entire planet and ends at one single instant. There is no American tithi and Indian tithi.

What differs is the clock you read it on.

Take the Chaturthi tithi that carries Karwa Chauth in 2026 — one continuous stretch of time, written down in local clocks:

One tithi. Three clocks. In Delhi it sits neatly inside the 29th. In Dubai it has already begun on the 28th. In Toronto it has largely finished by midday on the 29th — which is well before the moon comes up that evening.

And that last detail is exactly what decides your date.

The rule that decides which day a fast falls on

If a tithi can cover parts of two days, something has to pick one. That something is a rule called vyapini — literally "prevailing", as in prevailing at a particular moment.

Each observance has its own deciding moment, and the tithi has to be running at that moment. Not at any moment. At that one.

This is why Karwa Chauth shifts so dramatically while Ekadashi mostly does not. Sunrise comes early in the local day everywhere; moonrise and midnight come late, and late is where the timezone gap does its damage.

The panchangkar Pandit Mahesh Shastri states the Karwa Chauth case about as bluntly as it can be put:

“Chaturthi tithi appearing at the sunrise time cannot be taken if it appears on moonrise time on either days.”

— mypanchang.com. The rule belongs to the nibandha tradition — Nirnaya Sindhu and Dharma Sindhu — though we could not locate the exact passage in an edition of either, so treat it as what the panchang authorities state rather than a verified chapter-and-verse citation.

Having the tithi at sunrise is not enough. It has to be there when the moon comes up.

Worked example: Karwa Chauth 2026

Put the rule against real numbers and the pattern appears:

(From drikpanchang's own city pages, read on 22 September 2026.)

Now notice what the table does not say. It does not say "India one date, everywhere else another". London, Frankfurt and Sydney all keep India's date. Only North America moves.

Because the split is not about being abroad. It is about how many hours west of India you are — and Britain is four or five, while New York is nine and a half.

So the only question that matters is what the sky is doing above your own roof.

How to find the right date for your city

Two minutes, once a year. That is the entire method.

1. Open a panchang that lets you change city — drikpanchang or mypanchang. The link above is a live example.
2. Find the place selector near the top and type your city: Edison, Brampton, Wembley, Melbourne, Frankfurt, wherever you are.
3. The whole page recalculates. The date, the moonrise, the puja muhurat and the tithi window are now yours, not Delhi's.
4. Write down three things: the date, the deciding time (moonrise, or sunrise, depending on the festival), and the muhurat. A note on your phone is enough.
5. Do it a week early. Not on the evening itself.

Which festivals are most likely to shift

Go back to the vyapini table and the answer falls out: the later in the day the deciding moment is, the more likely your date moves.

One more thing that looks like a date difference and is not. North India ends the lunar month at the full moon (purnimanta); Gujarat, Maharashtra and the south end it at the new moon (amanta). So the same day gets called Kartik Krishna Chaturthi in one reckoning and Ashwin Krishna Chaturthi in the other. Same day, different label — if your family and the temple disagree on the month name but agree on the day, this is why.

Why the app on your phone shows India's date

Because almost every Indian festival app ships a single list of dates computed for Indian Standard Time, and simply displays it wherever you open it. It does not recompute for your longitude, because recomputing means running the actual ephemeris for your coordinates, and most apps are a calendar with a list in it.

They are not wrong. They are Indian calendars, doing what an Indian calendar does. The same goes for the WhatsApp forward from your aunt and the festival list at the back of an Indian magazine.

The test is simple: if a source never asked you where you live, it cannot be telling you your date. A panchang that lets you set a city is doing the calculation. Everything else is quoting Delhi.

When your family in India says a different day

This is the part that is never really about the calendar.

The short answer: you are both right. Your mother is giving you the date for the sky above her house, and you are using the date for the sky above yours. Observing on your own local date is not a departure from the tradition — it is the tradition's own rule, which says the tithi must be running at the deciding moment where you are.

The practical answer: do not argue, show. Open the same panchang she trusts, set it to your city, and send her the screenshot. It usually ends there.

And if it does not, keep her day. Nothing is lost by it, and peace in the family on a festival morning is worth more than being technically correct at eleven at night. Plenty of households have settled it exactly that way for years.

Frequently asked questions

Why is Diwali on a different date here than in India?

Because the Hindu calendar is tied to the moon, and the moment that decides a festival lands at a different local clock time in each country. Diwali's Lakshmi puja is fixed by the evening period after sunset, so if that period falls on one side of midnight in India and the other side where you live, the date moves. The tithi is the same everywhere; only the clock reading it changes.

What is a tithi?

A tithi is a lunar day — the time it takes for the angle between the Sun and the Moon to widen by 12 degrees. There are thirty in a lunar month. Crucially it is not 24 hours: it averages 23 hours 37 minutes and can run anywhere from about 20 hours to nearly 27, beginning and ending at any time of day rather than at midnight.

Is the Hindu calendar lunar or solar?

It is lunisolar — months are counted by the moon, years by the sun. Twelve lunar months come to about 354 days against a solar year of about 365, so an extra month called Adhika Masa is inserted roughly every 32.5 months to keep the two in step. That leap month is why a festival can fall in October one year and November the next.

How do I find the right festival date for my city?

Open a panchang that lets you change the location — drikpanchang or mypanchang — and type your own city into the place selector. The date, the moonrise or sunrise time and the puja muhurat all recalculate for your coordinates. Write down the date and the deciding time, and do it a week ahead rather than on the day.

Which festivals shift the most?

The ones decided late in the day. Karwa Chauth and Sankashti Chaturthi are fixed by moonrise, and Janmashtami and Mahashivratri by midnight — all of which fall far enough into the local day for a timezone gap to push them across a date boundary. Ekadashi and most weekday vrats are fixed by sunrise, which comes early everywhere, so they rarely move.

Why does my calendar app show India's date?

Because most Indian festival apps carry one list of dates computed for Indian Standard Time and display it unchanged wherever you open it. They are not wrong, they are simply Indian calendars. The test: if a source never asked where you live, it cannot be giving you your date.

My parents say a different day — who is right?

Both of you. They are using the date for the sky above their house and you are using the date for yours, and the rule itself says the tithi must be running at the deciding moment where you are. Rather than arguing, open the same panchang they trust, set it to your city and send the screenshot. And if that still does not settle it, keeping their day costs you nothing.

Can I observe on both days?

The tradition does not ask for it. A vrat rests on the sankalpa, the intention set for one specific day, and the whole purpose of the nirnaya tradition is to resolve a two-day tithi into a single day. Keeping a waterless fast two days running also asks something of the body that was never required. Pick one day and stay with it.

What are kshaya and adhika tithis?

Because a tithi is not 24 hours long, it sometimes begins after one sunrise and ends before the next, touching no sunrise at all — that is a kshaya tithi. Sometimes it is still running at two consecutive sunrises and so covers two days — that is an adhika tithi. Neither is inauspicious; both are simply arithmetic, and the vyapini rule exists to resolve exactly these cases.

What is the difference between amanta and purnimanta?

They are two ways of ending the lunar month, not two different dates. North India ends it at the full moon (purnimanta) while Gujarat, Maharashtra and the south end it at the new moon (amanta), so the same day is called Kartik Krishna Chaturthi in one system and Ashwin Krishna Chaturthi in the other. If your family and your temple agree on the day but disagree on the month name, this is why.

Sources and cautions: the lunisolar structure of the calendar — 354 days against 365, and the Adhika Masa correction roughly every 32.5 months — and the definition of a tithi as a 12° widening of the Sun–Moon angle are from the standard astronomical descriptions linked above. The vyapini rule and the sunrise-versus-moonrise sentence are quoted from mypanchang. All dates, moonrise times and tithi windows were read off drikpanchang's own city pages on 22 September 2026. We could not locate the exact Karwa Chauth passage in an edition of the Nirnaya Sindhu or Dharma Sindhu, so that rule is presented as what the panchang authorities state rather than as a chapter-and-verse citation. Panchangs differ by a few minutes — always check your own city.