Capital, Volume Three: The Process of Capitalist Production as a Whole by Karl Marx

For the purposes of the following analysis we may leave out of consideration the distinction between price of production and value, since this distinction disappears altogether when, as here, the value of the total annual product of labour is considered, i.e., the product of the total social capital.

Profit (profit of enterprise plus interest) and rent are nothing but peculiar forms assumed by particular parts of the surplus-value of commodities. The magnitude of surplus-value is the limit of the total size of the parts into which it may be divided. Average profit plus rent are, therefore, equal to the surplus-value.