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17/01/2018 09:01:29 AM

Activity-Based Costing VS Department Costing Systems

Activity-based costing (ABC) refines a costing system by identifying individual activities as the fundamental cost objects. An activityis an event, task, or unit of work with a specified purpose—for example, designing products, setting up machines, operating machines, and distributing products. More informally, activities are verbs; they are things that a firm does. To help make strategic decisions, ABC systems identify activities in all functions of the value chain, calculate costs of individual activities, and assign costs to cost objects such as products and services on the basis of the mix of activities needed to produce each product or service

Companies often use costing systems that have features of ABC systems—such as multiple cost pools and multiple cost-allocation bases—but that do not emphasize individual activities. Many companies have evolved their costing systems from using a single indirect cost rate system to using separate indirect cost rates for each department (such as design, manufacturing, distribution, and so on) or each subdepartment (such as machining and assembly departments within manufacturing) that can be thought of as representing broad tasks. ABC systems, with its focus on specific activities, are a further refinement of department costing systems. In this section, ABC systems and department costing systems.

Plastim uses the design department indirect cost rate to cost its design activity. Plastim calculates the design activity rate by dividing total design department costs by total parts-square feet, a measure of the complexity of the mold and the driver of design department costs. Plastim does not find it worthwhile to calculate separate activity rates within the design department for the different design activities, such as designing products, making temporary molds, and designing processes. Why? Because complexity of a mold is an appropriate cost-allocation base for costs incurred in each design activity. Design department costs are homogeneous with respect to this costallocation base.

In contrast, the manufacturing department identifies two activity cost pools—a setup cost pool and a machine operations cost pool—instead of a single manufacturing department overhead cost pool. It identifies these activity cost pools for two reasons. First, each of these activities within manufacturing incurs significant costs and has a different cost driver, setup-hours for the setup cost pool and machine-hours for the machine operations cost pool. Second, the S3 and CL5 lenses do not use resources from these two activity areas in the same proportion. For example, CL5 uses 75% (1,500 ÷ 2,000) of the setuphours but only 29.4% (3,750 ÷ 12,750) of the machine-hours. Using only machine-hours, say, to allocate all manufacturing department costs at Plastim would result in CL5 being undercosted because it would not be charged for the significant amounts of setup resources it actually uses.

Using department indirect cost rates to allocate costs to products results in similar information as activity cost rates if (1) a single activity accounts for a sizable proportion of the department’s costs; or (2) significant costs are incurred on different activities within a department, but each activity has the same cost driver and hence cost-allocation base (as was the case in Plastim’s design department).

From a purely product costing standpoint, department and activity indirect cost rates will also result in the same product costs if (1) significant costs are incurred for different activities with different cost-allocation bases within a department but (2) different products use resources from the different activity areas in the same proportions (for example, if CL5 had used 65%, say, of the setup-hours and 65% of the machine-hours). In this case, though, not identifying activities and cost drivers within departments conceals activity cost information that would be valuable for cost management and design and process improvements.