According to religious scriptures, on the day of Purnima of Shravan month, Raksha Bandhan is celebrated. As per Akhil Bhartiya Jyotish Parrishad, the festival of Raksha Bandhan is on August 20. This day the Bhadra constellation or yog is also being formed. However, since this Bhadra will be in Patal, it won’t be considered inauspicious.
Jyotish Parishad also says that celebrating Raksha Bandhan on August 21 is not orthodox.