Stamp duty is compulsory, but its calculation differs state to state depending upon the federal or municipality laws. Stamp duty is charged upon the agreement value. This can be based on carpet area or on built up area.  In Kolkata, stamp duty is based on the market value of the property as well as the area of the property. According to the website of the Directorate of Registration and Stamp Revenue Finance Department of the Government of West Bengal, one has to pay 6% stamp duty and 1% registration charges for a property valued at less than Rs 25 lakh and at 7% stamp duty and 1.1% registration charges for properties priced at more than Rs 25 lakh.