Several factors affect whether a cost is classified as direct or indirect:
Be aware that a specific cost may be a direct cost of one cost object but an indirect cost of another cost object. That is, the direct/indirect classification depends on the cost object that one is trying to determine the cost of. For example, the salary of an assembly department supervisor at Tesla is a direct cost if the cost object is the assembly department. However, because the assembly department assembles different models of electric cars, the supervisor’s salary is an indirect cost if the cost object is a specific product such as the Tesla Model 3 sedan. A useful rule to remember is that the broader the cost object definition—the assembly department, rather than the Model 3—the higher the direct cost portion of total costs and the more confident a manager will be about the accuracy of the resulting calculated cost.
One final point. A company can incur a cost—sacrifice a resource—without the cost being recorded in the accounting system. For example, certain retirement health benefits are only recorded in the accounting system after an employee retires although the cost is incurred while the employee is actually providing the service. Environmental costs are another example. Many companies, for example General Electric, have had to incur significant costs at a later date to clean up the environmental damage that was caused by actions taken several years earlier. To force managers to consider these costs when making decisions, some companies such as Novartis, the Swiss pharmaceutical giant, are imputing a cost in their cost accounting system for every ton of greenhouse gases emitted to surrogate for future environmental costs. These costs can be a direct cost of a product if they can be traced to a specific product. More commonly, these costs are associated with operating a manufacturing facility and cannot be traced to a specific product. In this case, they are indirect costs.