Every year the same conversation. When is Diwali actually? Someone's calendar says one date, someone's relatives in another state say a different one, and in 2024 the whole country genuinely could not agree — 31 October or 1 November, depending on whom you asked.
The rules behind this are precise. They are just not the rules most people assume.
The festival is fixed. The date is not.
Diwali is always Kartik Amavasya — the new moon of the month of Kartik. That never changes. What changes is where that falls on the Gregorian calendar you keep on your phone.
The Hindu calendar is lunisolar. Months follow the Moon: about 29.5 days from new moon to new moon. Twelve of those make roughly 354 days — eleven days short of the solar year. So every festival drifts about eleven days earlier each year, until the drift is corrected by inserting a whole extra month, the adhika masa, roughly every three years. That is why a festival can jump nearly three weeks later in one year and then creep backwards again.
The tithi is not a day
Here is the first thing that trips people up. A tithi — a lunar day — is not 24 hours. It is the time the Moon takes to gain 12 degrees on the Sun, and because both move at varying speeds, a tithi runs anywhere from about 19 to 26 hours.
Against a 24-hour civil day, two things follow:
- A tithi can begin and end between two sunrises and touch neither. It is skipped — kshaya.
- A tithi can stretch across two sunrises and be counted twice — vriddhi.
So seven days do not contain seven tithis, and Purnima and Amavasya do not strictly alternate. This is normal, correct, and the reason two calendars can disagree by a day without either being sloppy.
Amanta vs purnimanta: the trap
Now the part that catches even careful people, and the reason a “Kartik” label can be misleading.
India uses two different month-naming conventions. In the south and west, a month runs new moon to new moon — amanta. In much of the north, it runs full moon to full moon — purnimanta. The same fortnight can therefore carry two different month names.
Diwali is universally described as Kartik Krishna Amavasya, which is the purnimanta name. In the amanta system that identical new moon belongs to Ashwin. Take the popular name literally and feed it into an amanta calculation and you land a whole month late — behind Govardhan Puja, which is supposed to follow Diwali by a day. The festival ends up after its own sequel.
The names differ; the sky does not. Both traditions light the lamps on the same night.
Not every festival is judged at sunrise
The second trap, and the one that actually decides Diwali's date.
Most Hindu days are named for the tithi running at sunrise. But festivals are not all observed at sunrise, and each is judged at the moment its rite belongs to:
- Pradosh (dusk) — Diwali, Dhanteras, Holika Dahan
- Madhyahna (midday) — Ram Navami, Ganesh Chaturthi
- Aparahna (afternoon) — Dussehra
- Nishita (midnight) — Maha Shivaratri, Janmashtami
Diwali's Lakshmi Puja is a dusk rite, so the question is not “which day begins under Amavasya?” but “on which evening is Amavasya running at pradosh?” Judge it at sunrise instead and you will put Diwali a day out in most years.
This is exactly what happened in 2024. Amavasya straddled two evenings in an awkward way, different authorities weighted the pradosh window differently, and the country split between 31 October and 1 November. It was not confusion — it was a genuinely marginal case.
One more refinement: when a tithi touches two of the relevant windows, the rule is vyapini — “prevailing.” The correct day is the one with the greatest overlap of the window, not simply the first day it touches.
Why the Diwali week has uneven gaps
A nice consequence, and a good check that a calendar has been built properly. The five days of Diwali mix reference times: Dhanteras and Diwali are judged at pradosh, while Govardhan Puja and Bhai Dooj are judged at sunrise.
Because of that mixture, the gaps between them are not uniform. In 2026 they fall on 6, 8, 10 and 11 November — two days, then two, then one. That looks like an error and is not. A calendar that shows a perfectly even run has probably applied one reference time to everything.
And one thing that is nothing to do with the Moon
A final subtlety worth stating because it causes real errors: the astronomical instants behind all of this are computed in universal time, and India is 5 hours 30 minutes ahead. An event at 21:24 UTC is already the next day in India. Date an ingress or a tithi boundary without converting to IST first, and you will publish a festival a day early — correctly computed and still wrong.
Our dates
All of the above is why we compute festival dates from the Moon and Sun directly rather than copying a list, and then check them against published almanacs before publishing. You can see the full year on our festival calendar pages, alongside the daily panchang if you want the tithi for any given day.
And if you are choosing a date for something of your own rather than looking one up — a griha pravesh, a wedding, a launch — the same machinery is what the Muhurat Finder runs on, against your birth details rather than the country's calendar.
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