GDP can be determined in three ways, all of which should, in principle, give the same result. They are the production (or output or value added) approach, the income approach, or the expenditure approach. The most direct of the three is the production approach, which sums the outputs of every class of enterprise to arrive at the total. The expenditure approach works on the principle that all of the product must be bought by somebody, therefore the value of the total product must be equal to people’s total expenditures in buying things. The income approach works on the principle that the incomes of the productive factors (“producers,” colloquially) must be equal to the value of their product, and determines GDP by finding the sum of all producers’ incomes. The concept was in the news recently. To know more click the above link titled ‘Related News’.