National income is always measured in money, but there are a number of goods and services which are difficult to be assessed in terms of money. For example, painting as a hobby. by an individual, the bringing up of children by the mother, these services are not included in national income as remuneration is not given to them.
Also services of housewives and the services provided out of love, affection; mercy, sympathy and charity are not included in national income, as they are not paid for. By excluding all such services from it, the national income will work out to be less than what it actually is.