Chhath is kept with unusual rigour. Over four days the devotee, often a mother on behalf of her family, bathes and eats a single sattvic meal, then fasts without water for roughly thirty-six hours, and finally stands waist-deep in a river or pond to offer arghya, first to the setting Sun and again to the rising Sun the next morning. Offerings of thekua, fruit and sugarcane are carried to the water in bamboo baskets.
The festival begins on the fourth tithi of the waxing fortnight of Kartika with Nahay Khay, followed by Kharna on the fifth, the evening arghya on the sixth (Shashthi, which gives the festival its name), and the morning arghya on the seventh. The two arghya rites are fixed to local sunset and sunrise.
It originates in Bihar, Jharkhand and eastern Uttar Pradesh and the Mithila region of Nepal, and has spread with migration to cities across India and abroad.