When expenses (or costs) are viewed in relation to changes in output three distinct expense categories emerge (see Chapter 10):
1 Fixed expenses---Those expenses that are constant in total, from month to month, gardless of fluctuations in output or volume of work done. Because any expense can change, this concept must be applied (a) to a realistic or relevant range of output and (b) in relation to a given set of conditions (management policies, time constraints, and characteristics of the operation). Examples of fixed expenses are salaries, property taxes, insurance, and depreciation (straight-line).
2 Variable expenses---Those expenses that change in total, directly with changes in output or volume of work done. The output must be measured in terms of some activity base, such as units completed, direct labor hours, sales dollars, or number of service calls, depending on the activities in the responsibility center. Examples of variable costs in a factory direct materials, direct labor, and power usage.
3 Semivariable expenses---Those expenses that are neither fixed nor variable because they possess some characteristics of both. As output changes, semivariable expense change in the same direction but not in proportion to the change in output.