Differential analysis requires that you consider all differential revenues and costs—costs that differ from one alternative to another—when deciding between alternative courses of action.
Avoidable costs: Costs that can be avoided by selecting a particular course of action—are always differential costs and must be considered when deciding between alternative courses of action. Incremental analysis” and "differential analysis” are synonymous.
Opportunity costs: The benefits foregone when one alternative is selected over another—are differential costs, and must be included when performing differential analysis.
Sunk costs: Costs incurred in the past that cannot be changed by future decisions—are not differential costs because they cannot be changed by future decisions.
Direct fixed costs: Fixed costs that can be traced directly to a product line or customer—are differential costs and therefore pertinent to making decisions. However, you must review these costs on a case-by-case basis because some direct fixed costs may not be considered differential in spite of being traced directly to a product line. For example, a five-year lease on a warehouse used solely for one product line is a direct fixed cost but not a differential cost because the costs will continue even if the product line is eliminated.
Allocated fixed costs: Fixed costs that cannot be traced directly to a product—are typically not differential costs. For example, if a product line is eliminated, these costs are simply allocated to the remaining product lines.
When deciding between alternatives, only those revenues and costs that differ from one alternative course of action to another are relevant. Avoidable costs, opportunity costs, and direct fixed costs typically fall into this category. Revenues and costs that do not differ from one alternative course of action to another are irrelevant to the decision.