Where the value of supply is inclusive of integrated tax or, as the case may be, central tax, State tax, Union territory tax, the tax amount shall be determined in the following manner, 

Tax amount = (Value inclusive of taxes X tax rate in % of IGST or as the case may be CGST, SGST or UTGST) / (100+ sum of tax rates, as applicable, in %)

Explanation.- For the purposes of this Chapter,-

(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 price is the sole consideration, to obtain such supply at the same time when the supply being valued is made.

(b) “supply of goods or services or both of like kind and quality” means any other supply of goods or services or both made under similar circumstances that, in respect of the characteristics, quality, quantity, functional components, materials, and reputation of the goods or services or both first mentioned, is the same as, or closely or substantially resembles, that supply of goods or services or both.