Management Accounting · Marginal Costing (Management Accounting)

Marginal Costing Concepts and Cost Behaviour Explained

Updated 10 October 2026 · Fact-checked

Marginal costing treats only variable costs as product costs. Fixed costs are written off in full as period costs. Contribution is sales minus variable cost, and profit is contribution minus fixed cost. Absorption costing instead spreads fixed overheads over units, so closing stock is valued higher. Solve by splitting costs first, then building the statement.

Understand Marginal Costing Concepts and Cost Behaviour

Marginal cost is the change in total cost when output rises by one unit. In exam practice it is taken as the variable cost per unit: direct material, direct labour, direct expenses and variable overheads.

Cost behaviour means how cost changes with activity. A variable cost changes in total in proportion to output, but stays the same per unit. A fixed cost stays the same in total within the relevant range and period, so it falls per unit as output rises. A semi-variable cost has a fixed part and a variable part, such as a telephone bill with rental plus usage charge. A step cost stays fixed for a band of output and then jumps.

Contribution is sales minus variable cost. It is the amount each sale adds towards covering fixed cost and then profit. Until fixed cost is recovered, there is a loss. After that, each extra unit's contribution adds to profit.

In marginal costing, only variable cost goes into product cost and stock valuation. Fixed cost is charged to the period's profit as a whole. In absorption costing, fixed production overhead is also absorbed into each unit, so it moves into stock when units are unsold.

This is why the two methods can show different profits when opening and closing stock differ. When production equals sales, there is no stock change and profits are equal. The reconciliation of the two profits is a separate topic, but you need the concepts here first.

Key rules to remember

Marginal cost: Marginal cost = Direct material + Direct labour + Direct expenses + Variable overheads; Taken as variable cost per unit. Include variable selling and distribution cost when computing contribution.
Contribution: Contribution = Sales − Variable cost; Variable cost here includes variable production and variable selling costs.
Contribution per unit: Contribution per unit = Selling price per unit − Variable cost per unit; Multiply by units sold to get total contribution.
Profit: Profit = Contribution − Fixed cost; Fixed cost is the whole period's fixed cost, production and non-production.
Fixed cost per unit: Fixed cost per unit = Total fixed cost ÷ Units of output; Changes with output. It is why absorption costing unit cost changes with volume.
Stock valuation: Marginal costing: stock at variable production cost. Absorption costing: stock at variable plus absorbed fixed production cost; Non-production overheads are not included in stock in either method.
Profit difference: Difference in profit = Change in stock units × Fixed production overhead per unit; Valid when the overhead absorption rate is the same in the period. Absorption profit is higher when stock increases.

How to solve Marginal Costing Concepts and Cost Behaviour questions

Use this order for any question on marginal costing concepts, statements or the difference from absorption costing.

1Read the data and classify every cost as variable or fixed. Split semi-variable costs into their two parts.
2Separate production costs from selling and distribution costs, because only production costs go into stock.
3Compute variable cost per unit and contribution per unit.
4Prepare the marginal costing statement: Sales, less variable cost of goods sold (adjusted for stock), less variable selling cost, equals contribution, less total fixed cost, equals profit.
5If asked, prepare the absorption costing statement: add absorbed fixed production overhead to unit cost and value stock on that basis.
6Compare the profits and explain the reason in terms of stock change and fixed overhead carried forward.
7State the interpretation in one or two lines, for example what contribution shows or which method suits decisions.

Quickest way: Contribution-first shortcut

When to use it: Use for MCQs and for short questions asking for profit, contribution or the profit difference between the methods.

Write contribution per unit = price − variable cost per unit.
Profit under marginal costing = units sold × contribution per unit − total fixed cost.
If stock rises, absorption profit is higher by stock increase in units × fixed production overhead per unit.
If stock falls, absorption profit is lower by the same working.
If production equals sales, both profits are equal.

Common mistakes in Marginal Costing Concepts and Cost Behaviour

Treating all overheads as fixed or all labour as variable
Students classify by cost head instead of how the cost behaves.
Fix: Read the data for behaviour clues such as 'per unit' or 'per month'. Split semi-variable costs explicitly.
Leaving variable selling cost out of contribution
Students stop at production cost because that is how product cost is built.
Fix: Contribution = Sales − all variable costs, including variable selling and distribution. Only stock valuation uses production cost alone.
Including fixed cost in marginal costing stock values
Habit from absorption costing.
Fix: Value closing and opening stock at variable production cost only. Charge the full fixed cost to the period.
Valuing stock with selling overheads in absorption costing
Students think absorption means absorbing every overhead.
Fix: Absorb only production overheads into stock. Selling and distribution costs are period costs.
Calling contribution the same as profit
Both are shown as positive results in the statement.
Fix: Contribution is before fixed cost. Profit is contribution minus fixed cost.
Assuming fixed cost per unit is constant
Students remember that fixed cost is constant in total and forget the per unit effect.
Fix: Fixed cost is constant in total only. Per unit it falls as output rises.

Worked examples

Example 1

A company makes one product. Selling price is ₹50 per unit. Variable cost is ₹30 per unit (production ₹26, selling ₹4). Fixed cost is ₹2,00,000 per year. It sells 15,000 units. Find contribution per unit, total contribution and profit.

Show the solution

Contribution per unit = 50 − 30 = ₹20.
Total contribution = 15,000 × 20 = ₹3,00,000.
Profit = 3,00,000 − 2,00,000 = ₹1,00,000.

Answer: Contribution per unit is ₹20, total contribution is ₹3,00,000 and profit is ₹1,00,000.

Example 2

A firm produces 10,000 units and sells 8,000 units at ₹40 each. Variable production cost is ₹18 per unit and variable selling cost is ₹2 per unit sold. Fixed production overhead is ₹50,000 and fixed selling overhead is ₹30,000. There is no opening stock. Prepare profit under marginal costing and absorption costing, and explain the difference.

Show the solution

Marginal costing: sales = 8,000 × 40 = ₹3,20,000.
Variable production cost of units sold = 8,000 × 18 = ₹1,44,000. Variable selling cost = 8,000 × 2 = ₹16,000. Total variable cost = ₹1,60,000.
Contribution = 3,20,000 − 1,60,000 = ₹1,60,000.
Fixed cost = 50,000 + 30,000 = ₹80,000. Marginal costing profit = 1,60,000 − 80,000 = ₹80,000.
Absorption costing: fixed production overhead per unit = 50,000 ÷ 10,000 = ₹5. Production cost per unit = 18 + 5 = ₹23.
Cost of units sold = 8,000 × 23 = ₹1,84,000. Gross profit = 3,20,000 − 1,84,000 = ₹1,36,000.
Deduct selling costs: variable ₹16,000 and fixed ₹30,000, total ₹46,000. Absorption costing profit = 1,36,000 − 46,000 = ₹90,000.
Difference = 90,000 − 80,000 = ₹10,000. Closing stock is 2,000 units, and 2,000 × ₹5 = ₹10,000 of fixed production overhead is carried forward in stock under absorption costing.

Answer: Marginal costing profit is ₹80,000 and absorption costing profit is ₹90,000. The ₹10,000 difference is the fixed production overhead in 2,000 units of closing stock.

Exam tips

In MCQs, first check whether production equals sales. If it does, the two profits are equal and you can skip the long working.
In written answers, show the statement with clear lines: sales, variable cost, contribution, fixed cost, profit. Step marks follow these lines.
Always list stock valuation under each method separately, and state that selling overheads never enter stock.
Close theory questions with a brief interpretation, such as why marginal costing helps decisions while absorption costing is needed for external reporting and stock valuation.
For features and advantages, give four or five points with a one line reason each rather than a long list of headings.

Practice questions from Marginal Costing (Management Accounting)

Marginal Costing Concepts and Cost Behaviour in other exams

The same ground in other exams, if you are preparing for more than one or want another angle on it.

Marginal Costing Concepts and Cost Behaviour: frequently asked questions

What is contribution in marginal costing?

Contribution is sales minus variable cost. It is the amount available to cover fixed cost and then give profit. Profit equals contribution minus fixed cost.

What is the difference between marginal costing and absorption costing?

Marginal costing charges only variable cost to products and writes off all fixed cost in the period. Absorption costing also absorbs fixed production overhead into units and stock. Profits differ when opening and closing stock differ.

What are the main features of marginal costing?

Costs are split into fixed and variable. Only variable cost is charged to products and stock. Fixed cost is treated as a period cost. Contribution is the key measure and profit is found after deducting fixed cost from it.

What are the advantages of marginal costing?

It is simple to use and gives clear data for decisions such as pricing, product mix and make or buy. Profit follows sales, not stock changes, so it is not distorted by fixed cost moving in and out of stock. It also supports break-even and cost control.