These three methods of calculating GDP yield the same result because National Product = National Income = National Expenditure.
1. The Product Method:
In this method, the value of all goods and services produced in different industries during the year is added up. This is also known as the value-added method to GDP or GDP at factor cost by the industry of origin. The following items are included in India in this: agriculture and allied services; mining; manufacturing, construction, electricity, gas and water supply; transport, communication and trade; banking and insurance, real estates and ownership of dwellings and business services; and public administration and defense and other services (or government services). In other words, it is the sum of gross value added.
2. The Income Method:
The people of a country who produce GDP during a year receive incomes from their work. Thus GDP by income method is the sum of all factor incomes: Wages and Salaries (compensation of employees) + Rent + Interest + Profit.
3. Expenditure Method:
This method focuses on goods and services produced within the country for one year.
GDP by expenditure method includes:
(1) Consumer expenditure on services and durable and non-durable goods (C),
(2) Investment in fixed capital such as residential and non-residential building, machinery, and inventories (I),
(3) Government expenditure on final goods and services (G),
(4) Export of goods and services produced by the people of the country (X),
(5) Fewer imports (M). That part of consumption, investment and government expenditure which is spent on imports is subtracted from GDP. Similarly, any imported component, such as raw materials, which is used in the manufacture of export goods, is also excluded.
Thus GDP by expenditure method at market prices = C+ I + G + (X – M), where (X-M) is net export which can be positive or negative.