Absorption vs Marginal Costing and Profit Reconciliation

Learning objectives

By the end of this chapter you will be able to:

• Explain how absorption costing and marginal costing treat fixed production overhead and why reported profit can differ.
• Prepare profit statements under absorption costing and marginal costing, including correct inventory valuation.
• Reconcile the profit difference between the two methods using fixed production overhead carried in (or released from) inventory.
• Interpret how changes in inventory levels affect reported profit and performance signals.
• Assess when each method is most useful for planning, control, and short-term decision-making.

Overview & key concepts

Absorption costing and marginal costing are two common approaches to internal profit reporting for manufacturing businesses. They differ in one central area: how fixed production overhead is handled.

• Underabsorption costing(often calledfull costing), fixed production overhead is included in the cost of each unit produced and therefore can be held in inventory until the unit is sold.
• Undermarginal costing, fixed production overhead is not included in unit cost. It is charged in full against the period’s profit.

Because inventory can increase or decrease between periods, the amount of fixed production overhead charged to profit can differ even when sales and total fixed overhead are unchanged.

Absorption costing

What it means

Absorption costing includes:

• variable production costs (e.g. materials, variable labour, variable production overhead), and
• an allocated share of fixed production overhead

in the unit production cost.

Inventory values therefore include both variable manufacturing cost and an appropriate share of fixed manufacturing overhead. When inventory rises, some fixed production overhead is carried forward in closing inventory and is charged to profit in a later period when the goods are sold.

Unit cost under absorption costing

To build the unit cost:

• start with variable production cost per unit, then
• add fixed production overhead per unit (using an overhead absorption rate)

Fixed production overhead per unit = fixed production overhead / normal output (units)

Marginal costing

What it means

Marginal costing includes only variable production costs in the unit cost. Fixed production overhead is treated as a period cost and expensed in full in the period.

This produces a profit statement that highlights contribution, which is useful for short-term decision-making.

Contribution

Contribution is sales revenue less total variable costs. It shows how much is available first to cover fixed costs and then to generate profit.

Contribution = Sales − total variable costs

In a simple manufacturing example with no variable selling or distribution costs, total variable costs may equal variable cost of sales, so contribution can be calculated as sales minus variable cost of sales.

Profit under marginal costing:

Profit (marginal costing) = Contribution − Fixed costs

Fixed production overhead and the overhead absorption rate

Fixed production overhead (FPOH) includes manufacturing costs that do not change in total with short-term output, such as factory rent, production supervisors’ salaries, and factory depreciation.

Under absorption costing, FPOH is allocated to units produced using an overhead absorption rate (OAR):

OAR (per unit) = Budgeted (or expected) fixed production overhead / Normal output (units)

The fixed overhead charge per unit should be based on a sensible typical level of activity rather than an unusually weak or unusually busy month. This helps prevent unit costs (and therefore inventory values) being distorted by short-term swings in output.

When output is unusually low or unusually high, the per-unit allocation of fixed production overhead should not be allowed to create misleadingly high or low unit costs that would overstate or understate inventory values.

Inventory valuation and profit impact

Inventory valuation

• Absorption costing: inventory includes variable production costs + absorbed fixed production overhead.
• Marginal costing: inventory includes variable production costs only.

Why profit differs

The profit difference is driven by the amount of fixed production overhead carried in opening and closing inventory.

• If closing inventory is higher than opening inventory, absorption costing profit is higher because some fixed production overhead is carried forward in inventory.
• If closing inventory is lower than opening inventory, absorption costing profit is lower because previously deferred fixed production overhead is released into cost of sales.

Under- and over-absorption

Where an overhead absorption rate is used, the fixed overhead absorbed into production may differ from the fixed overhead actually incurred.

Compare actual fixed overhead incurred with fixed overhead absorbed:

• Ifactual exceeds absorbed:under-absorption
• Ifabsorbed exceeds actual:over-absorption

In many exam-style questions, budgeted and actual fixed production overhead are the same and output equals the level used to set the OAR, so there is no under/over absorption adjustment. Where the question indicates a difference, an adjustment may be required so profit and inventory are not misstated.

How the two methods affect profit reporting

Profit patterns and performance signals

Absorption costing can make profit appear to improve when production rises, even if sales do not. This happens because some fixed production overhead is transferred into inventory rather than being charged to the current period.

Marginal costing avoids this effect because fixed production overhead is charged in full to the period. Profit is therefore driven mainly by sales volume and contribution.

Double-entry logic (high-level)

Manufacturing cost flows are commonly tracked through inventory and cost of sales:

• Production costs accumulate in inventory (directly or via work in progress).
• When goods are sold, cost transfers from inventory to cost of sales.

The key distinction is whether fixed production overhead is included within inventory values (absorption) or charged directly as a period expense (marginal).

Internal vs external reporting

For published financial statements, unsold manufactured goods are normally measured using a production cost that includes variable manufacturing costs plus a reasonable share of fixed manufacturing overhead.

Marginal costing is different. It is mainly a management accounting tool used to support planning, control, and short-term decisions because it separates variable cost behaviour from fixed cost behaviour and makes contribution easier to see.

Exam tasks

Common tasks include:

• preparing profit statements under both methods,
• reconciling the profit difference, and
• commenting on whether profit changes reflect genuine trading improvement or are driven by inventory movement.

Worked example

Narrative scenario

A manufacturing company produces and sells a single product.

• Selling price: £50 per unit
• Variable production cost: £30 per unit
• Fixed production overhead: £40,000 per period (budgeted and incurred)
• Normal output: 10,000 units
• Fixed selling and administrative expenses: £12,000 per period

During the period:

• Opening inventory: 1,000 units
• Production: 10,000 units
• Sales: 9,500 units
• Closing inventory: 1,500 units

Required:

1. Calculate profit under marginal costing.
2. Calculate profit under absorption costing.
3. Reconcile the difference in profit.
4. Interpret the financial implications.

Solution

Step 1: Profit under marginal costing

Sales revenue:

9,500 units × £50 = £475,000

Variable production cost of sales:

9,500 units × £30 = £285,000

In this question there are no variable selling or distribution costs, so total variable costs equal variable production cost of sales.

Contribution:

Contribution = £475,000 − £285,000 = £190,000

Fixed costs:

• Fixed production overhead = £40,000
• Fixed selling and administration = £12,000
• Total fixed costs = £52,000

Profit (marginal costing):

£190,000 − £52,000 = £138,000

Step 2: Profit under absorption costing

Overhead absorption rate:

OAR = £40,000 / 10,000 units = £4 per unit

Absorption production cost per unit:

£30 + £4 = £34

Inventory valuation and cost of sales:

Opening inventory:
1,000 units × £34 = £34,000

Production cost:
10,000 units × £34 = £340,000

Goods available for sale:
£34,000 + £340,000 = £374,000

Closing inventory:
1,500 units × £34 = £51,000

Cost of sales:
£374,000 − £51,000 = £323,000

Gross profit:

£475,000 − £323,000 = £152,000

Less fixed selling and administration:

£152,000 − £12,000 = £140,000

Note: Fixed production overhead is not shown as a separate expense here because it is included within production cost and therefore within cost of sales, with part of it held in closing inventory.

Step 3: Reconcile the profit difference

The profit difference arises from the net movement of fixed production overhead into or out of inventory.

Change in inventory units:

Closing inventory 1,500 − Opening inventory 1,000 = +500 units

Fixed production overhead absorbed per unit:

£4 per unit

Net increase in fixed production overhead carried in inventory:

500 units × £4 = £2,000

Reconciliation:

Profit under absorption costing = £140,000
Less: net increase in fixed production overhead carried in inventory = £2,000
Profit under marginal costing = £138,000

Exam note: The shortcut approach below works where the profit difference is caused only by inventory movement:

Profit difference = Change in inventory units × Fixed production overhead absorbed per unit

If the question also includes under- or over-absorbed fixed overhead (because actual overhead differs from budget, or output differs from the level used to set the OAR), that adjustment must also be dealt with when comparing final profits.

Step 4: Interpretation of the results

Absorption costing reports the higher profit because inventory increased during the period. The increase of 500 units means that £2,000 of fixed production overhead is carried forward in closing inventory rather than being charged against this period’s profit.

When inventory rises, absorption costing can report a higher profit even if sales do not improve. Candidates should comment on whether profit growth reflects genuine operational improvement or is mainly driven by stock build-up.

Common pitfalls and misunderstandings

• Treating fixed production overhead as part of unit cost under marginal costing. Under marginal costing it is charged in full to the period.
• Valuing inventory incorrectly. Absorption costing includes absorbed fixed production overhead in inventory; marginal costing does not.
• Defining contribution too narrowly. Contribution is sales less total variable costs, which may include variable selling or distribution costs where relevant.
• Confusing contribution with profit. Contribution is before fixed costs.
• Using the wrong output level for the OAR. The rate is based on the output level stated in the question (commonly a typical or long-run activity level).
• Forgetting the direction of the reconciliation. If inventory increases, absorption profit exceeds marginal profit; if inventory falls, absorption profit is lower.
• Ignoring under/over absorption where output differs from the level used to set the OAR or actual overhead differs from budget.
• Interpreting higher absorption profit as better performance without considering whether the profit increase is linked to sales improvement or inventory build-up.

Summary

Absorption costing and marginal costing differ in the timing of recognising fixed production overhead:

• Absorption costing includes fixed production overhead in unit costs, so some fixed overhead can be carried in inventory when production exceeds sales.
• Marginal costing treats fixed production overhead as a period expense, so profit is more directly linked to sales volume and contribution.

The profit reconciliation hinges on inventory movement:

• Inventory increase → absorption profit higher
• Inventory decrease → absorption profit lower

Strong answers show clear mechanics (unit costs, inventory values, profit statements) and then add interpretation, especially where absorption profit rises due to stock build-up rather than stronger sales. Where under/over absorption exists, candidates should ensure that adjustment is also reflected when comparing profits.

FAQ

Why does absorption costing often show higher profit than marginal costing?

Because when inventory increases, part of the fixed production overhead is held in closing inventory under absorption costing and is not charged to the current period’s profit. Marginal costing charges all fixed production overhead in the current period, so it does not benefit from inventory increases.

How do inventory changes affect profit under the two methods?

Under absorption costing, inventory changes affect how much fixed production overhead is included in cost of sales versus carried in inventory. Under marginal costing, inventory changes do not change the total fixed production overhead charged to the period.

What is the overhead absorption rate and why does it matter?

It is the fixed production overhead allocated to each unit produced. It affects unit cost, inventory valuation, and cost of sales under absorption costing. An incorrect rate leads to incorrect profit and inventory figures.

Is marginal costing acceptable for external financial statements?

Marginal costing is mainly an internal reporting method. Published financial statements for manufacturers typically measure finished goods using production costs that include variable manufacturing costs plus an allocated share of fixed manufacturing overhead.

How do you reconcile profits between absorption and marginal costing?

Calculate the change in inventory units and multiply by the fixed production overhead absorbed per unit. This gives the net fixed overhead carried forward (or released) through inventory, but remember to consider any under/over absorption adjustment if the question includes it.

Profit difference = Change in inventory units × Fixed production overhead absorbed per unit

Glossary

Absorption costing
A method where unit production cost includes variable production costs plus an allocated share of fixed production overhead, so inventory includes both elements.

Marginal costing
A method where unit production cost includes only variable production costs. Fixed production overhead is treated as a period expense.

Fixed production overhead
Manufacturing costs that do not vary in total with short-term output (e.g. factory rent, production supervisors’ salaries).

Variable production cost
Production costs that increase with output (e.g. direct materials, variable labour, variable production overhead).

Contribution
Sales less total variable costs. It represents the amount available to cover fixed costs and then generate profit.

Inventory valuation
The cost assigned to unsold units. Under absorption costing it includes absorbed fixed production overhead; under marginal costing it includes only variable production cost.

Overhead absorption rate (OAR)
The rate used to allocate fixed production overhead to units produced.

Under-absorption
Occurs when actual fixed production overhead incurred is greater than the fixed overhead absorbed into production.

Over-absorption
Occurs when fixed overhead absorbed into production is greater than the actual fixed production overhead incurred.

Cost of sales
The cost of inventory sold in the period, charged to profit or loss.

Period cost
A cost charged in full to the period in which it is incurred rather than being carried in inventory (e.g. fixed production overhead under marginal costing).

Opening inventory / Closing inventory
Inventory at the start/end of the period. Changes between opening and closing inventory explain the profit difference between absorption and marginal costing methods.

Profit reconciliation
A calculation that explains the numerical difference between profits produced by absorption and marginal costing, driven by fixed production overhead held in (or released from) inventory.