absorption vs variable costing

Two factory managers cost the same product and disagree. One says each unit costs 24 dollars; the other says 18 dollars. They aren't arguing about the materials, labor, or even the variable overhead — they agree on all of that. The whole fight is about one thing: should each unit carry a slice of the factory's fixed overhead (rent, salaried supervisors, equipment depreciation), or should fixed overhead be treated as a cost of the period rather than of the product? That single question separates absorption costing from variable costing.

Absorption costing (full costing) treats all manufacturing costs as product costs: direct materials, direct labor, variable overhead, and a per-unit share of fixed overhead. Variable costing (direct costing) treats only variable manufacturing costs as product costs, and expenses all fixed manufacturing overhead immediately as a period cost. The practical consequence appears when production and sales differ. If a factory makes more than it sells, absorption costing parks some fixed overhead inside the unsold units in ending inventory, deferring that cost to a future period — so absorption income looks higher than variable-costing income. When sales exceed production, the reverse happens, and absorption income looks lower. When production equals sales, the two methods report the same income.

The distinction matters enormously. Absorption costing is required for external financial statements under both US GAAP and IFRS, and for tax. Variable costing is barred from those reports but is prized internally because it makes contribution margin and cost-volume-profit analysis clean and stops fixed-cost-per-unit numbers from shifting with volume. The honest warning baked into this comparison: under absorption costing a manager can raise reported profit simply by producing more units than are sold — building inventory shifts fixed overhead off the income statement and onto the balance sheet — which is a real and well-documented incentive problem that variable costing does not have.