As per Section 15(3)(a) the value of supply shall not include discount given before or at time of supply if such discount has been duly recorded on invoice issued for the supply. Further as per Sec 15(3)(b) even post discount can also be reduced from value subject to fulfillment of certain conditions. For details please refer to article “Understanding treatment of discount under GST Law”.
Frah Saeed Answered question May 10, 2020