Variable Costing and the Effect of Sales and Production
on Operating Income
Given a constant contribution margin per unit and constant fixed costs, the period-toperiod
change in operating income under variable costing is driven solely by changes in
the quantity of units actually sold. Consider the variable-costing operating income of
Stassen in (a) 2013 versus 2012 and (b) 2014 versus 2013. Recall the following:
Under variable costing, Stassen managers cannot increase operating income by “producing
for inventory.” Why not? Because, as you can see from the preceding computations,
when using variable costing, only the quantity of units sold drives operating income. We’ll
explain later in this chapter that absorption costing enables managers to increase operating
income by increasing the unit level of sales, as well as by producing more units. Before
you proceed to the next section, make sure that you examine Exhibit 9-3 for a detailed
comparison of the differences between variable costing and absorption costing.