The national income of a country for a given period is equal to the:

National Income is the total monetary value of goods and services produced within the territory of the country in a given period of time.
National Income = C+I+G+ (X-M)
Here, 
C stands for Consumption
I stands for Total Investment
G stands for Total Government Expenditure
X stands for Export
M stands for Import
Income Method: It is measured by adding four factors of production i.e. land, labour, capital, and entrepreneurship.
Production Method: Also known as the Value Added Method, national income is measured on the value of intermediate goods and final goods.

Expenditure Method: Also known as the Income Disposal Method, national income is measured by taking the final expenditure incurred by all sectors of the economy🔴Additional Information:
Dadabhai Naoroji was the first to estimate the National Income in the year 1867-68.
V.K.R.V Rao is known as the father of National Income in India. He introduced the first scientific estimate of national income in the year 1931-32. 
National Income Committee under the chairmanship of P.C Mahalanobis was appointed by the Government of India in 1949.