# Marginal product Marginal yield (green line): First of all, the additional benefit of each new unit increases, then at some point it decreases and becomes negative with excessive use

A marginal product (also marginal yield or marginal productivity ) is in neoclassical production theory the increase in yield (or benefit, cf. marginal utility ) that is achieved through the use of a further unit of a production factor . In mathematical terms, it is just the derivative of a function, e.g. B. the production function (cf. similar concepts for cost or benefit functions, see marginal costs and marginal utility).

In the neoclassical part of the yield law , the marginal yield of a production factor decreases steadily under otherwise identical conditions ( ceteris paribus ) (Fig. Phases 2 and 3). In the Cobb-Douglas production function , the marginal product of a variable factor is always positive but continuously falling.

## example

Someone works a field using different factors of production such as soil, labor, seeds and fertilizer . If he now increases the fertilizer factor, the yield (quantity of the harvested crop per area) rises first and thus the marginal fertilizer yield. If he uses more and more fertilizer, he realizes that plant growth cannot be increased at will: the marginal product (= the additional yield) is getting smaller and smaller. In the case of overfertilization , the yield of the crop per area even drops again, which then leads to a negative marginal fertilizer yield (extreme overfertilization can lead to the total loss of the cultivated fruit).

Negative marginal yields occur because one factor becomes increasingly disproportionate to the other factors.