When is Dhanteras?

How the date is decided

Dhanteras is Kartik Krishna Trayodashi — the thirteenth tithi of the waning fortnight of Kartik in the purnimanta reckoning.

The condition that fixes the civil day is pradosh: the period just after sunset. The Trayodashi has to be running then. A Trayodashi that begins at nine in the morning and ends before that evening’s sunset has not given the day a pradosh under Trayodashi, and the festival goes elsewhere.

This is the reference the Diwali cluster is built on, and it is chosen for the obvious reason — these are evening observances, lamps and all.

The cluster, and why the gaps vary

Four of the five days use pradosh; one does not:

Each is evaluated independently. Nothing in the calendar counts forward from Dhanteras to find Diwali. So while the sequence usually occupies five consecutive dates, that is a result rather than a rule — a short tithi that begins and ends between two sunsets can collapse a day out of the run, and a long one can double it up.

If you have ever seen an almanac print two festivals on one date in this week, this is why.

Why the month is called Kartik here

Dhanteras falls in the waning fortnight, which is exactly where the two lunar month conventions disagree. Under purnimanta reckoning the month runs full moon to full moon, placing this Trayodashi in Kartik. Under amanta reckoning it runs new moon to new moon, placing the same day in Ashwin.

Both are correct for their region and the date is unaffected. See amanta and purnimanta for the full split.

Why the Gregorian date moves

Dhanteras lands in late October or November. Twelve lunar months fall about eleven days short of a solar year, so the whole Diwali cluster drifts earlier annually until an intercalary month resets it. Major festivals are suppressed inside an Adhika month, so a leap Kartik shifts the sequence to the true Kartik rather than duplicating it.

On the day

The number that matters locally is sunset, since pradosh follows from it and it varies by more than an hour across the country. The panchang for your city gives sunset, the exact start and end of Trayodashi, and the day’s Rahu Kaal and choghadiya windows if you are choosing an hour rather than a day.

What we do not compute

We fix the day. We do not compute the Dhanteras puja muhurat, the purchase windows almanacs publish for the date, or the regional variants observed on their own rules.