Jyeshta Amavasya, the No Moon day in Jyeshta month, is also known as Vat Savitri Amavasya. Vat Amavasya Vrat is the major austerity of the month in various Hindu communities of Bengal, Orissa, Assam, Jharkhand, etc.
In 2015, Jyeshta Amavasya or Vat Savitri Amavasya Vrat date is May 18 in North Indian calendar except Marathi and Gujarati calendars.
For Telugu, Kannada, Gujarati, and Marathi people, Jyeshta Amavasya 2015 date is June 16.
Jyeshta Amavasya is also observed as Falharini Kali Puja in West Bengal, some parts of Orissa and Assam.