SingaporeAccountingSyllabus dot point

Why do marginal and absorption costing give different profits, and how is the difference reconciled?

Reconcile the profit reported under marginal and absorption costing and explain the effect of inventory changes

A focused answer to the H2 Principles of Accounting outcome on reconciling the two methods. Why profits differ when inventory changes, the fixed-overhead-in-inventory effect, the reconciliation, and which method suits which purpose.

Generated by Claude Opus 4.810 min answerUpdated 2026-06-06

Reviewed by: AI editorial process; not yet individually human-reviewed

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What this dot point is asking
The answer
Examples in context
Try this

What this dot point is asking

SEAB wants you to reconcile the profit reported under marginal and absorption costing and to explain why they differ when inventory changes. This is a favourite exam topic because it tests whether you truly understand how each method treats fixed overhead. The central insight is that the only difference between the two profits is the fixed overhead carried in the change in inventory: marginal costing expenses all fixed overhead now, while absorption costing defers some of it in unsold units.

The answer

Why the profits differ

Both methods recognise the same sales and the same variable costs. They differ only in how fixed production overhead is treated:

Marginal costing charges all fixed overhead as a period cost in the period incurred.
Absorption costing attaches fixed overhead to units, so any fixed overhead in unsold units is carried forward in closing inventory.

When inventory changes, a different amount of fixed overhead is expensed under each method, so the profits differ by exactly that amount.

The rule linking inventory change to profit

The relationship depends on whether inventory rises or falls:

Situation	Inventory	Absorption profit versus marginal
Production > sales	Rises	Higher (overhead deferred in inventory)
Production < sales	Falls	Lower (overhead released from inventory)
Production = sales	Unchanged	Equal

When production exceeds sales, absorption costing defers fixed overhead in the extra inventory, so it reports a higher profit. When sales exceed production, opening inventory's deferred overhead is released and expensed, so absorption profit is lower.

The reconciliation

The difference is always the fixed overhead in the change in inventory:

\text{Difference in profit} = \text{change in inventory units} \times \text{fixed overhead per unit}

So:

\text{Absorption profit} = \text{Marginal profit} + (\text{increase in inventory} \times \text{fixed overhead per unit})

(with a decrease in inventory reducing absorption profit instead).

Which method for which purpose

Absorption costing is required for external reporting, because standards require inventory at full production cost. Marginal costing is preferred for internal decisions, because contribution focuses on the costs that change and is not distorted by inventory movements. Understanding both, and how to move between them, is the goal of this dot point.

Worked example

A firm has fixed overhead absorbed at $\$ 8 $per unit. In a period it produces$ 15,000 $units and sells$ 17,000 $(so opening inventory existed). Marginal costing profit is$ \ $90\,000$ . Reconcile to absorption costing profit.

Step 1: Find the change in inventory

Sales ( $17\,000$ ) exceed production ( $15\,000$ ), so inventory falls by $17\,000 - 15\,000 = 2\,000$ units.

Step 2: Fixed overhead released

The $2\,000$ -unit fall releases fixed overhead held in opening inventory: $2\,000 \times 8 = \$ 16,000$. This overhead, deferred in a previous period, is now expensed under absorption costing.

Step 3: Apply the reconciliation

A fall in inventory makes absorption profit lower than marginal:

\text{Absorption profit} = 90\,000 - 16\,000 = \$74\,000

Step 4: Interpret

Absorption costing reports $\$ 74,000 $,$ \ $16\,000$ below marginal costing, because selling more than was produced released previously deferred fixed overhead into this period's expenses. Had production instead exceeded sales, absorption profit would have been higher. The reconciling figure is always the fixed overhead in the inventory change.

Examples in context

Example 1. Building stock to flatter profit. A manager under absorption costing could raise reported profit by producing more than is sold, deferring fixed overhead in the growing inventory. Marginal costing prevents this, because all fixed overhead is expensed regardless of production. This is a key reason marginal costing is preferred internally: absorption profit can be manipulated through stock levels, which short-run decisions must not reward.

Example 2. A clear-out year. A company that ran down its accumulated stock sells far more than it produces in a year. Under absorption costing, the fixed overhead locked in that opening inventory is released and expensed, depressing reported profit even though trading was strong. Reconciling to marginal costing reveals the underlying contribution was healthy, showing why analysts adjust for inventory movements when judging performance.

Try this

Q1. Inventory rises by $1\,500$ units and fixed overhead is $\$ 10$ per unit. State the effect on absorption profit versus marginal profit. [2 marks]

Cue. Absorption profit is higher by $1\,500 \times 10 = \$ 15,000$, because that overhead is deferred in the increased inventory.

Q2. Marginal profit is $\$ 60,000 $; inventory falls by$ 1,000 $units; fixed overhead is$ \ $7$ per unit. Find absorption profit. [3 marks]

Cue. A fall lowers absorption profit: $60\,000 - (1\,000 \times 7) = 60\,000 - 7\,000 = \$ 53,000$.

Q3. Explain why the two methods give the same profit when production equals sales. [2 marks]

Cue. With no change in inventory, no fixed overhead is deferred or released, so the same total fixed overhead is expensed under both methods and the profits are identical.

Exam-style practice questions

Practice questions written in the style of SEAB exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.

Original7 marksA company produces

10\,000

units and sells

8\,000

. The fixed overhead absorption rate is

\

per unit. Marginal costing profit is

40\,000

. (a) Calculate the absorption costing profit. (b) Explain the cause of the difference.

Show worked answer →

(a) Inventory rose by $10\,000 - 8\,000 = 2\,000$ units. Under absorption costing, each unit in inventory carries fixed overhead of $\$ 6 $, so$ 2,000 \times 6 = \ $12\,000$ of fixed overhead is carried forward in closing inventory instead of being expensed this period.

Absorption profit $=$ marginal profit $+$ fixed overhead in the increase in inventory $= 40\,000 + 12\,000 = \$ 52,000$.

(b) The difference arises because production exceeded sales, so inventory increased. Marginal costing charges all fixed overhead as a period cost, but absorption costing defers $\$ 12,000 $of it in the unsold units. Absorption profit is therefore$ \ $12\,000$ higher this period; that deferred overhead will be expensed when the units are sold next period.

Markers reward the $2\,000$ -unit inventory increase, $\$ 12,000 $of fixed overhead deferred, absorption profit of$ \ $52\,000$ , and the explanation that production exceeding sales causes the gap.

Original6 marksExplain how profit under marginal and absorption costing compares when (a) production exceeds sales, (b) sales exceed production, and (c) production equals sales. State which method is preferred for decision making and why.

Show worked answer →

The difference depends on the change in inventory and the fixed overhead it carries.

(a) Production exceeds sales (inventory rises): absorption profit is higher, because fixed overhead is deferred in the increase in closing inventory rather than all expensed.

(b) Sales exceed production (inventory falls): absorption profit is lower, because fixed overhead from previous periods, held in opening inventory, is now released and expensed.

(c) Production equals sales (no inventory change): the two methods give the same profit, because no fixed overhead is deferred or released.

For decision making, marginal costing is preferred, because it isolates contribution and treats fixed costs as period costs, so decisions are based on the costs that actually change. Absorption profit can be distorted by inventory changes, which is misleading for short-run decisions.

Markers reward the three comparisons tied to inventory movement, the equal-profit case, and marginal costing for decisions with the contribution reasoning.