Anant Dwadashi Vrat is observed in Bhadrapada Month. It is a very rarely heard Vrata which is dedicated to Lord Vishnu.
It begins on Shukla Paksha Dwadashi of Bhadrapada Month (two days prior to Ananta Chaturdashi) and is observed for one year. The major ritual of this vrata is year-long ‘Vishnu Puja’.
The merits of this Vrata include – Ananta Phaladayakam (Infinite merits) and Moksha (Salvation).
Ananta Dwadashi Vrata is mentioned in Vishnudharmottara Purana and Hemadri Vratakhand.