Why does national income include only final goods ?

Explanation

Intermediate goods are not included in the national income to avoid double counting. The value of intermediate goods is already included in the final goods. If the value of intermediate goods is added again, it will lead to double counting . For example, the value of shirt (final good) includes the value of cloth (intermediate good). So, if we include the value of cloth along with the value of shirt, it will lead to double counting of cloth.