In calculation of GDP, there are some important things to consider. We must avoid double counting so that the same product should not be included twice in calculation of GDP. It is useful to exclude some final goods and services from GDP for some practical reasons. Especially, some goods and services not being marketed (such as services provided by housewives) are not included into GDP. The second feature of GDP is that it includes all final goods and services produced in the economy. The transactions which are completely financial are not included into GDP. Second hand sales of goods are not taken into account in GDP calculation. GDP indicates the production realized within the borders of a country, but does not refer to the value of production realized by production factors belonging to citizens of the country.