How is the date of Diwali determined?

Answer 1

The date for Diwali is decided upon the Hindu calendar, which is based on the phases of the moon.

Diwali falls on the one new moon night (Amavasya) between mid-October and mid-November. Diwali is celebrated for five days according to the lunisolar. It begins in late Ashvin (between September and October) and ends in early Kartika (between October and November). The days in Ashvin are in the Krishna Paksha ("dark fortnight") of that month, while the days in Kartik are in its Shukla Paksha ("bright fortnight"). The first day is Dhan Teras. The last day is Yama Dvitiya, which signifies the second day of the light half of Kartika. Each day of Diwali marks one celebration of the six principal stories associated with the festival.

Answer 2

Date of Diwali is determine as the first amavas after Dushhera. Amavas is the day 15 after full moon.