Gst on flat purchased

No, if flat is having completion certificate.......  i.e. ready to move in.

Transfer of completed property is not considered as rendering services to a buyer and thus does not attract GST. According to the CBEC's clarification, “Sale of building is an activity or consideration which is neither a supply of goods nor a supply of services. (Para 5 of schedule III of the CGST Act, 2017).” So if you buy a completed property, it will help you save money in form of tax.

Refer:  cbec/gst/GST_on_property

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