What you'll learn
Absorption costing and marginal costing are two ways of deciding what a unit of output costs, and they differ on exactly one question: what to do with fixed production overhead.
Absorption costing treats fixed production overhead as part of the cost of making a unit. Every unit carries a share of it, absorbed at a predetermined rate, and that share stays with the unit into inventory. Marginal costing treats fixed production overhead as a cost of the period rather than of the units, so inventory is valued at variable production cost only and the whole fixed overhead is charged against the period in which it was incurred.
The consequence is that the two methods report different profits whenever inventory changes — and the difference is exactly the fixed overhead sitting in the change in inventory. That relationship is examined in almost every question on the topic, and being able to state it and prove it is worth more than either calculation on its own.
By the end of this topic you should be able to prepare both statements, reconcile the profit difference, explain when each method is appropriate, and say why marginal costing is the one used for short-run decisions.
Key terms and definitions
Absorption costing — fixed production overhead is absorbed into units and carried in inventory. Also called full costing or total costing.
Marginal costing — inventory is valued at variable production cost; fixed production overhead is charged in full to the period.
Contribution — sales revenue less variable costs. What each unit contributes towards covering fixed costs and then towards profit.
Contribution per unit — selling price per unit less variable cost per unit.
Fixed production overhead absorption rate — budgeted fixed production overhead divided by budgeted production, used to attach fixed overhead to units under absorption costing.
Period cost — a cost charged in full to the period in which it arises, rather than attaching to units.
Profit reconciliation — the statement explaining the difference between the two reported profits by reference to the change in inventory.
Core concepts
The single point of difference
Both methods treat variable production costs identically, and both charge selling, distribution and administration costs to the period. The only disagreement is fixed production overhead.
Under absorption costing it is a product cost: it attaches to units and is therefore carried forward in closing inventory into the next period. Under marginal costing it is a period cost: it is charged in full now, whatever happens to inventory.
Everything else in the topic follows from that one sentence, and a candidate who can state it precisely can usually reason out any question in the area.
Why profits differ, and by how much
If production exceeds sales, inventory rises. Under absorption costing, some fixed overhead attaches to those unsold units and is carried forward, so it does not reduce this period's profit — absorption profit is higher. Under marginal costing it was all charged now.
If sales exceed production, inventory falls, and fixed overhead carried in from last period is released into cost of sales — absorption profit is lower.
If inventory does not change, both methods report the same profit.
The difference is always:
change in inventory units × fixed production overhead absorbed per unit
Quoting that formula and then demonstrating it with the figures is the reliable way to secure the reconciliation marks.
The marginal costing statement
The marginal statement is built around contribution. Sales, less variable production cost of sales, less variable selling costs, gives contribution. All fixed costs are then deducted in one block to give profit.
Its advantage is that contribution is visible, and contribution is what decision-making needs. If a business is asked to accept an extra order at a reduced price, what matters is whether the price exceeds the variable cost — the fixed overhead will be incurred either way, so it is irrelevant to that decision.
The absorption costing statement
The absorption statement looks like an ordinary income statement. Sales, less cost of sales at full production cost, gives gross profit; less non-production costs, gives profit.
Its advantage is that it complies with accounting standards for external reporting, because inventory must be valued to include an appropriate share of production overhead. It also ensures that, over the long run, prices set from full cost cover all costs.
Its disadvantage for internal use is that profit becomes sensitive to production volume rather than sales volume. Producing more units than can be sold raises reported profit by parking fixed overhead in inventory, which is an incentive worth being aware of.
Over the long run the methods agree
It is worth being clear that absorption costing does not create profit and marginal costing does not destroy it. Fixed production overhead is charged against profit in full under both methods; they disagree only about which period bears it.
Across the whole life of a business, or across any run of periods that begins and ends with the same inventory, the two methods report exactly the same total profit. A period in which inventory rises and absorption profit is higher is always followed, eventually, by a period in which that inventory is sold and absorption profit is correspondingly lower.
This matters for two reasons. It is the answer to a student who suspects one method must be overstating profit — neither is. And it identifies where the real concern lies: not in the total, but in the fact that absorption profit in any single period responds to how much was produced as well as how much was sold. A manager judged on one year's absorption profit has an incentive to produce for inventory, and recognising that incentive is a strong evaluation point.
When each is appropriate
Use absorption costing for external financial statements, inventory valuation and long-run pricing, where all costs must eventually be covered.
Use marginal costing for short-run decisions — accepting a special order, dropping a product line, choosing between products competing for a scarce resource — because only the costs that change between the alternatives are relevant.
The two are not rivals. A business can prepare marginal statements for management and absorption statements for publication, reconciling between them.
Worked examples
Example 1 — The two statements compared (10 marks)
A business produces 10,000 units and sells 8,000 at $50 each. Variable production cost is $30 per unit. Fixed production overhead is $80,000, and fixed selling costs are $20,000. There was no opening inventory.
Marginal costing: Sales = 8,000 × $50 = $400,000. Variable cost of sales = 8,000 × $30 = $240,000. Contribution = $400,000 − $240,000 = $160,000. Less fixed costs: $80,000 + $20,000 = $100,000. Profit = $160,000 − $100,000 = $60,000.
Closing inventory = 2,000 × $30 = $60,000.
Absorption costing: Fixed overhead per unit = $80,000 ÷ 10,000 = $8.00. Full production cost per unit = $30 + $8 = $38.00. Sales = $400,000. Cost of sales = 8,000 × $38 = $304,000. Gross profit = $400,000 − $304,000 = $96,000. Less fixed selling = $20,000. Profit = $96,000 − $20,000 = $76,000.
Closing inventory = 2,000 × $38 = $76,000.
Example 2 — Reconciling the difference (4 marks)
Absorption profit $76,000 against marginal profit $60,000 — a difference of $16,000.
Reconciliation: inventory rose by 2,000 units, each carrying $8.00 of fixed production overhead. 2,000 × $8.00 = $16,000.
That $16,000 of fixed overhead is sitting in closing inventory under absorption costing, so it has not yet been charged against profit. Under marginal costing it was charged in full this period. The inventory values confirm it: $76,000 against $60,000, the same $16,000 apart.
Production exceeded sales, so absorption profit is the higher of the two — which is the general rule, not a coincidence of these figures.
Example 3 — The reverse case (4 marks)
In the following period the business produces 7,000 units and sells 9,000, running inventory down from 2,000 to nil. The rate remains $8.00 per unit.
Inventory fell by 2,000 units, so 2,000 × $8.00 = $16,000 of fixed overhead carried in from last period is released into cost of sales.
Absorption profit is therefore $16,000 lower than marginal profit in this period.
Taken across the two periods together the total profit is identical under both methods. The methods differ in when fixed overhead hits profit, never in how much of it does.
Example 4 — Why marginal costing for a decision (5 marks)
The business is offered a one-off order for 1,000 units at $34 each. Absorption costing says each unit costs $38, so the order appears to lose $4 a unit.
Marginal costing asks a different question. Variable cost is $30, so contribution is $34 − $30 = $4 per unit, or $4,000 in total. The $80,000 of fixed overhead will be incurred whether the order is taken or not, so it is irrelevant to this decision.
Accepting the order therefore adds $4,000 to profit, provided spare capacity exists and the price does not undermine the regular market. Rejecting it on the strength of the $38 full cost would have been the wrong call — and is the classic trap this topic sets.
Common mistakes and how to avoid them
Treating fixed selling costs as absorbable. Only fixed production overhead is absorbed into units.
Valuing closing inventory at full cost under marginal costing. Marginal inventory is at variable production cost only.
Getting the direction of the difference backwards. Production above sales means inventory rises and absorption profit is higher.
Calculating the difference from the profit figures alone. Prove it as change in inventory units × fixed overhead per unit; the mark is for the reconciliation, not the subtraction.
Using budgeted production instead of actual to value inventory. The absorption rate comes from budget; the units valued are the actual ones held.
Rejecting a special order because the price is below full cost. Compare it with variable cost, since fixed overhead is unavoidable either way.
Claiming one method is correct. Each answers a different question; the choice depends on the purpose.
How this links to your Internal Assessment
If the business you studied holds inventory of finished goods, preparing both statements is a strong analytical section, because the reconciliation demonstrates something an owner rarely appreciates: reported profit depends partly on how much was produced, not only on how much was sold.
The more useful application is decision-making. Find a real decision the business faced or could face — a bulk order at a discount, a product line the owner suspects is unprofitable — and analyse it on contribution rather than full cost. Then state the conditions your recommendation depends on: spare capacity exists, the discounted price will not leak into the regular market, and the fixed costs genuinely will not change.
Naming those conditions is what distinguishes an analysis from an assertion, and it protects you if the owner's circumstances differ from your assumptions.
Exam technique for absorption and marginal costing
Questions almost always ask for both statements and then the reconciliation. Prepare them side by side rather than sequentially, because the sales figure and the variable costs are identical and copying them once saves time and avoids transcription errors.
Calculate the fixed overhead absorption rate first and label it. Everything in the absorption statement depends on it, and an unlabelled rate makes the rest of the working impossible for an examiner to follow.
State the closing inventory figure under each method. It is usually worth a mark in itself and it provides the cross-check for the reconciliation.
Watch the command words. Prepare wants both statements in proper form. Reconcile wants the change in inventory multiplied by the fixed overhead per unit, not a subtraction of the two profits. Explain why the profits differ wants the product-cost versus period-cost distinction. Advise on a special order wants contribution, the assumption of spare capacity, and a stated recommendation.
If the question gives opening inventory as well as closing, work with the change between them, and check whether the absorption rate was the same in both periods — if it changed, the reconciliation needs each period's own rate.
Quick revision summary
- The only difference is the treatment of fixed production overhead: product cost under absorption, period cost under marginal.
- Marginal inventory is valued at variable production cost; absorption inventory at full production cost.
- Production above sales: inventory rises, absorption profit is higher.
- Sales above production: inventory falls, absorption profit is lower.
- No change in inventory: both profits are the same.
- Difference = change in inventory units × fixed production overhead per unit.
- Over the life of the business, total profit is identical under both — only the timing differs.
- Contribution = sales less variable costs, and it is what short-run decisions turn on.
- Use absorption for external reporting, inventory valuation and long-run pricing.
- Use marginal for special orders, dropping a line, and scarce-resource choices.
- A price below full cost can still be worth accepting if it exceeds variable cost and capacity is spare.