Variable Costing

In variable costing, a manufacturer charges to each unit produced only the costs that vary with production volume—raw materials, direct labor, and variable manufacturing overhead. All fixed costs (facility rent, salaried supervisors, depreciation on equipment) are treated as period expenses and deducted against total revenue for the period, not allocated to individual units. This method contrasts with absorption costing, the standard under US generally accepted accounting principles.

Element	Treatment under Variable Costing
Raw materials	Assign to product
Direct labor	Assign to product
Variable overhead	Assign to product
Fixed overhead	Expense in period incurred
Inventory valuation	Excludes fixed costs
Income measure	Affected by unit sales, not production

The mechanics of unit cost under variable costing

In variable costing, the cost assigned to a single unit equals direct material cost plus direct labor cost plus variable overhead cost per unit. If a factory produces 1,000 units and incurs $20,000 in materials and labor, each unit carries a $20 variable cost. Fixed overhead—say, $100,000 in annual rent—is never attached to units; instead, it is subtracted in aggregate from the company’s total contribution margin for the period. As a result, ending inventory on the balance sheet appears lower under variable costing than under absorption costing, because fixed costs are not capitalized into inventory value.

How variable costing affects reported profit

The divergence between variable and absorption costing becomes stark when production and sales volumes differ. Suppose a company produces 10,000 units but sells only 8,000. Under absorption costing, the 2,000 unsold units carry their share of fixed overhead, inflating inventory on the balance sheet and deferring those fixed costs into future periods as a deferred tax liability or inventory write-down. Under variable costing, all fixed overhead for the period is expensed immediately, so reported profit depends only on units sold, not units manufactured. A manufacturer using variable costing who over-produces will see no artificial profit boost from absorbing fixed costs into inventory.

Why variable costing is preferred for internal decisions

Internal management often prefers variable costing for decisions because it isolates the contribution margin—revenue minus variable costs—which directly shows the cash each unit generates to cover fixed costs and profit. This metric is invaluable for pricing decisions, make-or-buy analysis, and capacity planning. If a unit’s contribution margin is positive, producing it adds value; if it is negative, producing it destroys value. Variable costing makes these calculations transparent, whereas absorption costing obscures them by bundling fixed costs into every unit.

Regulatory status and GAAP constraints

Variable costing is not permitted for external financial reporting under US GAAP or IFRS. Public companies must use absorption costing in their audited financial statements. However, companies routinely maintain both systems in parallel: absorption costing for external reports and tax filings, variable costing for budgets, forecasts, and strategic decisions. Some analysts restate reported earnings to a variable costing basis when analyzing a manufacturer’s profitability and pricing power.