Absorption costing treats fixed manufacturing overhead as a product cost: it attaches to each unit made, and GAAP requires it for external financial statements. Variable costing treats the same fixed overhead as a period cost, expensed in full in the month it is incurred, and is used internally for decisions. Operating income differs between the two whenever inventory levels change — by exactly the fixed overhead per unit times the change in inventory units.
Everything else is identical. Direct materials, direct labor, and variable manufacturing overhead are product costs under both methods, and selling and administrative expenses are period costs under both. The entire disagreement is one line: where fixed manufacturing overhead goes.
Kestrel Cookware makes cast-iron skillets. In March it produced 8,000 skillets and incurred, per unit, $11 of direct materials, $7 of direct labor, and $3 of variable manufacturing overhead. Fixed manufacturing overhead for the month was $96,000 — $12 per unit at 8,000 units produced ($96,000 ÷ 8,000).
| Cost component | Absorption costing | Variable costing |
|---|---|---|
| Direct materials | $11 | $11 |
| Direct labor | $7 | $7 |
| Variable manufacturing overhead | $3 | $3 |
| Fixed manufacturing overhead ($96,000 ÷ 8,000) | $12 | — (period cost) |
| Product cost per unit | $33 | $21 |
Kestrel sold 6,500 of the 8,000 skillets at $42 each, so 1,500 units ended March in inventory (there was no beginning inventory). Selling and administrative costs were $2 per unit sold plus $38,400 fixed. The absorption statement groups costs by function: cost of goods sold first, then selling and administrative. The variable statement groups costs by behavior: all variable costs come out first to show contribution margin, then every fixed cost is deducted as a period expense.
| Line item | Absorption costing | Variable costing |
|---|---|---|
| Sales (6,500 × $42) | $273,000 | $273,000 |
| Cost of goods sold (6,500 × $33) | (214,500) | — |
| Variable cost of goods sold (6,500 × $21) | — | (136,500) |
| Variable selling & administrative (6,500 × $2) | — | (13,000) |
| Gross margin | 58,500 | — |
| Contribution margin | — | 123,500 |
| Selling & administrative ($13,000 + $38,400) | (51,400) | — |
| Fixed manufacturing overhead | — | (96,000) |
| Fixed selling & administrative | — | (38,400) |
| Net operating income (loss) | $7,100 | $(10,900) |
The $18,000 gap is not an error. It is fixed overhead sitting in ending inventory. Under absorption costing, each of the 1,500 unsold skillets carries $12 of fixed overhead onto the balance sheet as an asset: 1,500 × $12 = $18,000 of March's fixed overhead that never reached the income statement. Under variable costing, the full $96,000 was expensed in March, sold or not.
| Reconciliation | Amount |
|---|---|
| Variable costing net operating income (loss) | $(10,900) |
| Add: fixed overhead deferred in ending inventory (1,500 × $12) | 18,000 |
| Absorption costing net operating income | $7,100 |
The rule generalizes. When production exceeds sales, inventory grows, fixed overhead is deferred, and absorption income is higher. When sales exceed production, inventory shrinks, and absorption income is lower — the $12 stored in each old unit flows out through cost of goods sold on top of the current month's fixed overhead. When production equals sales, the two methods report the same income.
Absorption costing is the external method. GAAP and IFRS both require it for financial statements, and U.S. tax rules require it for inventory, because inventory is supposed to carry the full cost of producing it — the fixed overhead is expensed when the unit sells, not when it happens to be made. Variable costing is the internal method. Cost-volume-profit analysis, special-order pricing, and break-even work all need to know which costs move with volume, and the variable format keeps fixed overhead visible as one lump sum instead of burying $12 of it in every unit.
Absorption costing also carries a known incentive problem: producing more than you sell raises reported income. If Kestrel's manager had produced 9,600 skillets instead of 8,000 — with the same 6,500 sold — fixed overhead per unit would fall to $10 ($96,000 ÷ 9,600), more of it would be deferred into inventory, and absorption income would jump from $7,100 to $20,100 without one extra skillet sold. The extra profit is deferral, not performance, and the cost of carrying the extra 1,600 units is real. This is why exam questions ask you to reconcile the two incomes, and why companies that evaluate managers on absorption income watch inventory levels.
First, misclassifying selling costs. The name "variable costing" suggests every variable cost goes into the unit, but only variable manufacturing costs do. Kestrel's $2 per-unit selling cost is a period cost under both methods — it sits above the contribution margin line on the variable statement, but it never enters inventory under either method.
Second, flipping the reconciliation direction. Memorizing "absorption is higher" fails the moment inventory shrinks. Reason from the inventory instead: fixed overhead rides into inventory when production outruns sales and rides out when sales outrun production. The sign of (units produced − units sold) tells you which income is higher, every time.
Third, using the absorption unit cost for volume decisions. The $33 looks like what one more skillet costs, but $12 of it is fixed overhead that does not change when one more unit is made. A special order at $30 per skillet reads as a $3 loss under absorption costing, yet it covers the $21 variable product cost with $9 to spare — the absorption number would have you reject profitable work. Volume decisions belong to variable costing.
The two methods disagree on one line only: absorption costing attaches fixed manufacturing overhead to units ($12 each here); variable costing expenses it as incurred. Income differs by fixed overhead per unit × the change in inventory units — $12 × 1,500 = $18,000 when Kestrel built 1,500 units of inventory.
No. Selling and administrative costs — fixed or variable — are period costs under both absorption and variable costing. Absorption costing only absorbs manufacturing costs into units: direct materials, direct labor, and both variable and fixed manufacturing overhead.
Matching. GAAP treats inventory as an asset that carries the full cost of producing it, including a fair share of fixed manufacturing overhead, so the cost is expensed in the period the unit is sold rather than the period it was made. IFRS and U.S. tax rules take the same position.
It depends on inventory. When production exceeds sales, absorption income is higher because some fixed overhead is deferred into ending inventory. When sales exceed production, variable costing income is higher. When production equals sales, both methods report the same income.
Direct materials + direct labor + variable manufacturing overhead + fixed manufacturing overhead per unit, where the last term is total fixed manufacturing overhead divided by units produced. In the example: $11 + $7 + $3 + ($96,000 ÷ 8,000) = $33 per unit.
Yes. Direct costing and marginal costing are older names for the same method: variable manufacturing costs are treated as product costs, and fixed manufacturing overhead is expensed as a period cost in the month incurred.
By the FinanceBrain Team · Last verified July 11, 2026 · How we produce and verify articles