Diwali, the festival of lamps, centres on Lakshmi Puja on the new-moon night of the autumn month. In the Purnimanta calendar used across much of North India this is Kartika Amavasya; in the Amanta calendar the same night is Ashwin Amavasya. It is one date described in two ways (see Amanta and Purnimanta).

The basic rule: Amavasya in Pradosh

Lakshmi Puja is traditionally performed in Pradosh Kaal, which begins at sunset and lasts one fifth of the night. Diwali is therefore observed on the evening when Amavasya prevails during Pradosh. Within that window, many Panchangs also recommend a Sthira (fixed) lagna, commonly Vrishabha, which usually rises during the early evening, as a stable time for the puja.

When Amavasya covers two evenings

Amavasya can last long enough to touch Pradosh on two consecutive evenings. The rule applied on this platform is:

  • The second evening is chosen only if Amavasya continues for at least one ghati (24 minutes) into that evening's Pradosh.
  • Otherwise the first evening is taken.
  • If Amavasya covers Pradosh on neither evening, the day on which Amavasya prevails the longest is used as a fallback.

The five days of Diwali

Diwali is usually celebrated as a sequence of five days, each with its own timing rule:

  1. Dhanteras: Trayodashi prevailing in Pradosh; Dhanvantari and Lakshmi-Kuber puja.
  2. Naraka Chaturdashi (Choti Diwali): Chaturdashi at Arunodaya, with the traditional oil bath before sunrise.
  3. Diwali (Lakshmi Puja): Amavasya in Pradosh, as described above.
  4. Govardhan Puja: Kartika Shukla Pratipada in the morning, with Annakut.
  5. Bhai Dooj: Shukla Dwitiya, traditionally observed in Aparahna.

Because each day follows its own rule, the five observances do not always fall on five consecutive dates.

Why cities and Panchangs sometimes disagree

Amavasya ends at the same instant everywhere, but sunset does not. A city in the east reaches Pradosh earlier than one in the west, so the length of overlap on each evening changes with location, and in close years the chosen evening can differ between cities. Dharmashastra authorities also weigh the two evenings differently, and some regional traditions, such as Kali Puja in Bengal, look at midnight rather than Pradosh. Traditions may vary by region and Panchang convention, so check your local Panchang where it matters.

See the date and Pradosh timings for your city on the Diwali page.