Maha Dwadashi is an auspicious vrat which is observed in Bhadrapada Month. In 2018, Maha Dwadashi date is September 21. It falls on Bhadrapada Shukla Dwadashi.
This Vrata is considered even more auspicious if it falls on Shravana Nakshatra. And if it falls on Wednesday, it is highly meritorious. And when it falls on the combination day of Shravana Nakshatra and Wednesday (Budhwar), then it is considered the merit of observing the vrata is equals to that of ‘Mantra Japa on ten Surya Grahan’.
Lord Vishnu is worshipped with Shodashopachar Puja on this day. Upavaas (fasting) is also observed on this day.
Vishudharmottarapuran has mentioned the importance of Shravan Dwadashi in elaborated way. ‘Krityaratnakara’ is also mentioned about this vrata.