Section 35(a) in The Central Goods and Services Tax Rules, 2017
(a)"open market value" of a supply of goods or services or both means the full value in money, excluding the integrated tax, central tax, State tax, Union territory tax and the cess payable by a person in a transaction, where the supplier and the recipient of the supply are not related and the price is the sole consideration, to obtain such supply at the same time when the supply being valued is made;
