Vishnu Panchaka Upavasa is observed by a staunch Vishnu devotee and is dedicated to Lord Vishnu. As part of Vishnu Panchaka Upavasa, a devotee fasts and does pujas and rituals on five days in a traditional Hindu month. The five days are the two ekadashis, on Poornima (full moon), Amavasya (No moon) and on the Shravana Nakshatra day.
The popular belief is that Vishnu Panchaka Upavasa will help in the removal of sins committed. It is also performed for happy and peaceful life.
A devotee wishing to start Vishnu Panchaka Upavasa must make sure that all the five fasting days are present in that particular month (as per traditional Hindu calendar).
Usually people start Vishnu Panchaka Upavasa on the Ekadasi day falling during the waxing phase of moon in Margashirsh Month (December – January).
The Vrat can also be started if the Shukla Paksha Ekadasi in Bhadra month (waxing phase of moon in Bhadrapad month {August – September}) coincides with Shravana nakshatra.