How does buying/selling houses affect the GDP? Suppose I buy a house and sell it off in the same year for the same price, would the GDP for that year increase by twice the value of the house, or only once, or not at all?
There is only a change in GDP to the extent there are market goods and services used in the sale and only those goods and services are counted. The actual sales revenue are irrelevant. For example, the home inspection, appraisal, brokerage fees, and, I believe mortgage closing costs, would be in GDP. If you and your sister swapped houses in as-is condition without getting the market, bank, or tax authority involved, there would be no change in GDP.