Valuation Rules of GST -CGST Rules 2017 - Rule 27

Rule 27 - Value of Supply of goods or services where the consideration is not wholly in money

Where the supply of goods or services is for a consideration not wholly in money, the value of the supply shall, - 

a) Be the Open Market Value of such supply,
[ Open Market Value means the full value in money, (excluding GST) where the supplier and the recipient are not related and price is the sole consideration, to obtain such supply at the same time when the supply being valued is made.] 
Example - Suppose a mobile phone comes in market for 15,000/- and you exchange it for another old mobile phone and pay extra 10,000/-, the as per Rule 27, value of new mobile phone is Rs 15,000/-.

b) If the Open Market Value is not available under clause (a), be the Sum Total of Consideration in money and any such further amount in money as is equivalent to the consideration not in money, if such amount is known at the time of supply,
Example - Suppose a newly launched Car you are planning to purchase in exchange of another old Car, then its Open Market Value is not available it is not available in the market. So if the resale value of old car is Rs 5 lakh and in addition to old car you are paying Rs 2 lakh, then the value of new car is Rs 7 lakh. 

c) If the value of supply is not determinable under clause (a) or clause (b),  be the value of supply of goods or services or both of like kind and Quality.
Example - Suppose a Maruti Swift you are purchasing and the value cannot be determined under clause (a) and clause (b), then the car of same quality, same characteristics, functional, components and material use as of Maruti Swift can be used for valuation under clause (c).

d) If the value is not determinable under clause (a), clause (b) or clause (c), be the sum total of consideration in money and such further amount in money that is equivalent to consideration not in money as determined by the application of Rule 30 or Rule 31 in that order.