Section 15 of the CGST Act, 2017 specifies that the value of supply of goods or services or both shall be the transaction value, which is the price actually paid or payable for the said supply of goods or services or both where the supplier and the recipient of the supply are not related and the price is the sole consideration for the supply. Further, Section 15 provides for certain inclusions which will form part of the value viz., incidental expenses, commission, interest, penalty etc. In cases where the supplier and recipient are related persons or where the price is not the sole consideration, the provisions and method for ascertaining the value of taxable supply as prescribed in the Central Goods and Services Tax Rules (“the CGST Rules” or “the CGST Rules, 2017”) (Rules 27 – 35) shall apply.
(ICAI FAQ PUBLICATION 06-09-2017 LEVY AND COLLECTION: FAQ NO. 14)