What is the Right Costing Method for Decisions?
Managers must choose between absorption costing and variable (marginal) costing when making internal decisions. Absorption costing is required for external financial reporting, but variable costing isolates the contribution margin and gives better information for short-term choices.
For short-term decisions, variable (marginal) costing is preferred because it separates fixed and variable costs and shows the contribution margin; absorption costing is required for external financial reporting under GAAP/IFRS.
- •Includes fixed & variable manufacturing overhead in product cost
- •Required for external reporting (GAAP/IFRS)
- •Income affected by production volume
- •Fixed overhead deferred in inventory
- •Includes only variable manufacturing costs in product cost
- •Used for internal management decisions
- •Income tracks sales volume, not production
- •Fixed overhead expensed in the period incurred
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Step-by-step worked examples
A company produces 12,000 units and sells 10,000 units; the fixed overhead rate is $5/unit. Find the income difference.
Qp − Qs = 12,000 − 10,000 = 2,000 Difference = 2,000 × $5 = $10,000 (absorption income is higher)
Production is 8,000 units, sales are 9,000 units, with a fixed overhead rate of $4/unit.
Qp − Qs = 8,000 − 9,000 = −1,000 Difference = −1,000 × $4 = −$4,000 (absorption income is lower)
Regular price is $50, variable cost is $30 (contribution margin $20). Should a special order at $35/unit be accepted with idle capacity?
Special order price ($35) exceeds variable cost ($30) Extra contribution of $5/unit → accept (fixed costs are already covered)
Flashcards
Quick quiz
Q1.Under absorption costing, if units produced exceed units sold, reported operating income is generally:
Q2.Which costing method is required for external financial reporting under GAAP/IFRS?
Q3.In a special order decision with idle capacity, which cost is most relevant?
Q4.If units produced = units sold, absorption and variable costing operating income will be:
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Common mistakes
Believing fixed manufacturing overhead should be included in the incremental cost of a special order. — Correct: Fixed overhead already committed is irrelevant to short-term decisions when capacity is idle — use variable cost only.
Assuming absorption and variable costing always give the same operating income. — Correct: They differ whenever production volume ≠ sales volume, because absorption costing defers/releases fixed overhead in inventory.
Using variable costing net income for external financial statements. — Correct: GAAP/IFRS require absorption costing for external reporting; variable costing is for internal decisions only.
Treating all fixed costs as irrelevant in every decision. — Correct: Fixed costs are irrelevant only if they truly don't change with the decision; avoidable fixed costs are relevant.
FAQ
What is the right costing method for business decisions?
For internal decisions, variable (marginal) costing is preferred because it separates fixed and variable costs and highlights the contribution margin; absorption costing is used for external reporting.
What is the formula for the difference between absorption and variable costing income?
Difference = (Units produced − Units sold) × Fixed overhead rate per unit.
What are examples of choosing a costing method for decisions?
Special order acceptance, make-or-buy choices, and product-line profitability all rely on variable/relevant costing rather than full absorption cost.
How do you calculate which costing method to use for a decision?
Identify costs that change with the decision (relevant/variable costs) and ignore sunk or unavoidable fixed costs; compare incremental revenue to incremental cost.