There is concept known as surplus value. It is value created by the unpaid labor of wage workers, over and above the value of their labor power, and appropriated without compensation by the capitalist. Surplus value is a specific expression of the capitalist form of exploitation, in which the surplus product takes the form of surplus value. The production and appropriation of surplus value constitute the essence of the fundamental economic law of capitalism. In reality, surplus value is manifested as profit.
In their boundless desire to increase the production of surplus value, the capitalists intensify the exploitation of wage workers in various ways. There are two forms of surplus value— relative surplus value and absolute surplus value, each of which is associated with a method of intensifying the exploitation of the workers. Absolute surplus value is the result of lengthening the workday beyond the necessary labor-time or the time in which the worker can reproduce the value of his labor power. The actual length of the workday depends on the relation of class forces. Motivated by an avid desire to increase surplus value, the capitalists do their utmost to prolong the workday. However, as its level of organization improves, the working class, through stubborn struggle, gains legislation limiting the workday. Absolute surplus value also increases as a result of increasing the intensity of labor, even if the length of the workday remains the same or is shortened. The development of capitalism is characterized by a persistent increase in the rate of surplus value, which is the relationship between the total mass of surplus value and variable capital, or between surplus labor-time and necessary labor-time. This relationship is expressed as a percentage in the formula sʹ = s/v, in which s’ is the rate of surplus value, s is the mass of surplus value, and v is the variable capital. There is a functional connection between the mass and rate of surplus value. If the rate of surplus value reflects the degree of exploitation of the working class, the mass of surplus value reflects the absolute magnitude (s) of surplus value and equals the value of the variable capital (v) advanced, multiplied by the rate of surplus value (sʹ). Marx observed that “the rate of surplus value is therefore an exact expression for the degree of exploitation of labor power by capital, or of the worker by the capitalist”.