Karva Chauth is celebrated on the fourth day (chaturthi tithi) after the full Moon in the month of kartik in the Hindu calendar. According to the religious scriptures like Dharma sindhu, Nirnay sindhu and other shastra that governs rules of when to observe festival says, “Karwa Chauth to be observed at moonrise (chandrodaya vyapini) and poorvaviddha, best if its tritiya viddha. If visible during both days take the first one, if not visible on both days then take the second one”.