Time-Driven Activity-Based Costing
n the classroom, activity-based costing looks like a great way to manage a company’s limited resources. But many managers who have tried to implement ABC in their organizations on any significant scale have abandoned the attempt in the face of rising costs and employee irritation. They should try again, because the new approach we lay out in the following pages sidesteps the difficulties traditionally associated with large-scale ABC implementation by relying on informed managerial estimates rather than on employee surveys. It also provides managers with a far more flexible cost model to capture the complexity of their operations.
ABC Made Difficult
The roots of the problem with ABC lie in the way people traditionally construct ABC models. Assume you are analyzing a customer service department that performs three activities: processing orders, handling inquiries, and performing credit checks. The department’s total expenses (the cost of the personnel, management, IT, telecommunications, and other fixed resources) amount to $560,000. The actual (or estimated) quarterly quantities of work in the three activities are 49,000 orders, 1,400 inquiries, and 2,500 credit checks.
The New ABC
The solution to the problems with ABC is not to abandon the concept. ABC after all has helped many companies identify important cost- and profit-enhancement opportunities through the repricing of unprofitable customer relationships, process improvements on the shop floor, lower-cost product designs, and rationalized product variety. Its potential on a larger scale represents a huge opportunity for companies. Fortunately, simplification is now possible through an approach that we call time-driven ABC, which we have successfully helped more than 100 client companies implement, including those described in this article. In the revised approach, managers directly estimate the resource demands imposed by each transaction, product, or customer rather than assign resource costs first to activities and then to products or customers. For each group of resources, estimates of only two parameters are required: the cost per time unit of supplying resource capacity and the unit times of consumption of resource capacity by products, services, and customers. At the same time, the new approach provides more accurate cost-driver rates by allowing unit times to be estimated even for complex, specialized transactions.
In the revised approach, managers directly estimate the resource demands imposed by each transaction, product, or customer.
Estimating the cost per time unit of capacity.
Instead of surveying employees on how they spend their time, managers first directly estimate the practical capacity of the resources supplied as a percentage of the theoretical capacity. There are various ways to do this. As a rule of thumb, you could simply assume that practical full capacity is 80% to 85% of theoretical full capacity. So if an employee or machine is available to work 40 hours per week, its practical full capacity is 32 to 35 hours per week. Typically, managers would allot a lower rate—say 80%—to people, allowing 20% of their time for breaks, arrival and departure, communication, and training. For machines, managers might allot a 15% differential between theoretical and practical capacity to allow for downtime due to maintenance, repair, and scheduling fluctuations. A more systematic approach, perhaps, is to review past activity levels and identify the month with the largest number of orders handled without excessive delays, poor quality, overtime, or stressed employees. Whichever approach you prefer, it’s important not to be overly sensitive to small errors. The objective is to be approximately right, say within 5% to 10% of the actual number, rather than precise. If the estimate of practical capacity is grossly in error, the process of running the time-driven ABC system will reveal the error over time.
Returning to our example, let’s assume that the customer service department employs 28 reps to do the frontline work and that each puts in eight hours per day. In theory, therefore, each worker supplies about 10,560 minutes per month or 31,680 minutes per quarter. The practical capacity at about 80% of theoretical is therefore about 25,000 minutes per quarter per employee, or 700,000 minutes in total. Since we already know the cost of supplying capacity—the $560,000 in overhead costs—we can now calculate the cost per minute of supplying capacity ($0.80).
The capacity of most resources is measured in terms of time availability, but the new ABC approach can also recognize resources whose capacity is measured in other units. For example, the capacity of a warehouse or vehicle would be measured by space provided, while memory storage would be measured by megabytes supplied. In these situations, the manager would calculate the resource cost per unit based on the appropriate capacity measure, such as cost per cubic meter or cost per megabyte.
Estimating the unit times of activities.
Having calculated the cost per time unit of supplying resources to the business’s activities, managers next determine the time it takes to carry out one unit of each kind of activity. These numbers can be obtained through interviews with employees or by direct observation. There is no need to conduct surveys, although in large organizations, surveying employees may help. It is important to stress, though, that the question is not about the percentage of time an employee spends doing an activity (say, processing orders) but how long it takes to complete one unit of that activity (the time required to process one order). Once again, precision is not critical; rough accuracy is sufficient. In the case of our example, let’s suppose that managers determine that it takes 8 minutes to process an order, 44 minutes to handle an inquiry, and 50 minutes to perform a credit check.
Deriving cost-driver rates.
The cost-driver rates can now be calculated by multiplying the two input variables we have just estimated. For our customer service department, we obtain cost-driver rates of $6.40 (8 multiplied by $0.80) for processing customer orders, $35.20 (44 by $0.80) for handling inquiries, and $40 (50 by $0.80) for performing credit checks. Once you have calculated these standard rates, you can apply them in real time to assign costs to individual customers as transactions occur. The standard cost rates can also be used in discussions with customers about the pricing of new business.
Note that these rates are lower than those estimated using traditional ABC methods (see again the exhibit “Doing ABC the Traditional Way”). The reason for this difference becomes obvious when we recalculate the quarterly cost of performing the customer service activities. In the exhibit “The Impact of Practical Capacity,” time-driven ABC analysis reveals that only 83% of the practical capacity (578,600 of the 700,000 minutes) of the resources supplied during the quarter has been used for productive work, and hence, only about 83% of the total expenses of $560,000 were assigned to customers or products during this period. This takes care of the technical drawback of traditional ABC systems we mentioned earlier—the fact that surveyed employees respond as if their practical capacity were always fully utilized.