Editing Marginal cost (section)

== Short run marginal cost ==
[[File:Short run marginal cost.png|thumb|Short Run Marginal Cost]]
Short run marginal cost is the change in total cost when an additional output is produced in the short run and some costs are fixed. On the right side of the page, the short-run marginal cost forms a U-shape, with quantity on the x-axis and cost per unit on the y-axis.

On the short run, the firm has some costs that are fixed independently of the quantity of output (e.g. buildings, machinery). Other costs such as labor and materials vary with output, and thus show up in marginal cost. The marginal cost may first decline, as in the diagram, if the additional cost per unit is high, if the firm operates at too low a level of output, or it may start flat or rise immediately. At some point, the marginal cost rises as increases in the variable inputs such as labor put increasing pressure on the fixed assets such as the size of the building. In the long run, the firm would increase its fixed assets to correspond to the desired output; the short run is defined as the period in which those assets cannot be changed.