Variable cost Sound applet Variable cost equals total cost minus fixed cost. The variable cost is extra cost of producing Q, above the cost of producing 0. Here are the variable costs for screening mammograms. The costs in this table vary with the output rate, so they are variable costs. Variable cost graphed Sound applet Variable cost goes up in parallel with total cost.
Marginal cost is the additional cost of producing one more.
Or the reduction in cost from producing one less. The technologist is somewhat of a fixed cost over small changes in output rate, unless you can hire a part-time technologist. There's no allowance for that in these numbers, so let's assume that you can only hire full-time technologists. Sound applet To start with marginal cost, let's put the technologist's costs aside for a moment, and first do the marginal cost for the items for which we have unit costs. Those are straightforward.