Cost and Management Accounting · Marginal Costing

Marginal Costing Concepts and Cost Behaviour

Updated 4 October 2026 · Fact-checked

Marginal costing charges only variable costs to products and treats fixed costs as period costs written off in the period. Contribution is sales minus variable cost. Profit is contribution minus fixed cost. To solve questions, split costs by behaviour, find contribution, then deduct fixed cost.

Understand Marginal Costing Concepts and Cost Behaviour

Marginal cost is the change in total cost when output changes by one unit. In practice, ICAI-style questions treat it as the variable cost per unit: direct material, direct labour, direct expenses and variable overheads.

Marginal costing is a technique where only variable costs are charged to cost units. Fixed costs are not absorbed into products. They are treated as period costs and written off in full against the contribution of the period.

This works because of cost behaviour. A variable cost changes in total with output but stays constant per unit. A fixed cost stays constant in total within a relevant range of output and a given period, but 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. A step cost stays fixed over a band of output and then jumps, such as a supervisor needed for every extra 500 units.

Contribution is sales minus variable cost. It is the amount available to cover fixed costs and then give profit. When contribution equals fixed cost, profit is nil. This is why marginal costing is so useful for pricing, make-or-buy and product mix decisions.

Marginal costing values closing stock at variable cost only. This is the key difference from absorption costing, where stock also carries a share of fixed cost.

Key rules to remember

Contribution: Contribution = Sales − Variable cost; Per unit: Contribution per unit = Selling price per unit − Variable cost per unit.
Profit: Profit = Contribution − Fixed cost; Also: Sales − Variable cost − Fixed cost. A negative result is a loss.
Fixed cost from data: Fixed cost = Contribution − Profit; Useful when profit and sales are given and fixed cost is missing.
Variable cost per unit: Variable cost per unit = Change in total cost ÷ Change in units; High-low method for splitting a semi-variable cost. Use the highest and lowest activity levels, not highest and lowest costs unless they coincide.
Fixed cost per unit: Fixed cost per unit = Total fixed cost ÷ Units produced; It changes with output. Total fixed cost does not (within the relevant range).
Stock valuation: Stock value (marginal costing) = Units × Variable cost per unit; Fixed cost is never included in stock under marginal costing.

How to solve Marginal Costing Concepts and Cost Behaviour questions

Use this method for any numerical or theory question on marginal costing concepts.

1Read the data and list every cost item given.
2Classify each cost as variable, fixed or semi-variable. Split semi-variable costs using the high-low method or the split given.
3Compute variable cost per unit by adding all variable items, including variable selling and distribution costs.
4Compute contribution per unit and total contribution at the given sales volume.
5Deduct total fixed cost from total contribution to get profit.
6Value closing stock, if asked, at variable cost per unit only.
7For theory parts, state the point, give a one-line reason and a short example. Use bullet points for features, advantages and limitations.
8Check that fixed cost has not been put into per-unit cost or stock anywhere.

Quickest way: Contribution first, then fixed cost

When to use it: Use in MCQs and short numericals where you need profit, fixed cost or contribution quickly.

Write one line: Sales − VC = C; C − FC = P. Fill in whatever is given.
Work with per-unit figures first, then multiply by units.
For MCQs, eliminate options that include fixed cost in unit cost or stock valuation under marginal costing.
If an option shows contribution lower than variable cost or profit higher than contribution, reject it.
In written answers, show a neat statement: Sales, less variable cost, contribution, less fixed cost, profit. Each line earns a step mark, even if the final figure slips.

Common mistakes in Marginal Costing Concepts and Cost Behaviour

Including fixed overhead in closing stock valuation under marginal costing.
Students carry over the habit from absorption costing and cost sheets.
Fix: Under marginal costing, stock is at variable cost only. Fixed cost is charged in full to the period.
Treating contribution as profit.
Both are 'what is left from sales' and the words sound alike.
Fix: Contribution is before fixed cost. Profit is after fixed cost. Always deduct fixed cost as the last step.
Leaving out variable selling and distribution costs from variable cost.
Students think only production costs are variable.
Fix: Include every cost that varies with units sold, such as sales commission on units or packing, when computing contribution.
Saying fixed cost per unit is constant.
Students mix up 'fixed in total' with 'fixed per unit'.
Fix: Fixed cost is constant in total, but per unit it falls as output rises. Variable cost is the opposite: constant per unit, changing in total.
Using highest and lowest cost figures instead of highest and lowest activity in the high-low method.
Students pick the biggest and smallest numbers in the cost column.
Fix: Pick the periods with highest and lowest output, then use their costs to find the variable rate.
Writing one-sided answers on limitations, or listing points without explanation.
Students memorise headings only.
Fix: Write each point with a short reason, for example: 'Ignores fixed cost in stock, so profit may be understated when stock rises.'

Worked examples

Example 1

A company sells 10,000 units at ₹50 per unit. Direct material is ₹15, direct labour ₹10 and variable overhead ₹5 per unit. Variable selling expense is ₹2 per unit. Fixed costs are ₹1,80,000. Find the contribution per unit, total contribution and profit.

Show the solution

Variable cost per unit = 15 + 10 + 5 + 2 = ₹32.
Contribution per unit = 50 − 32 = ₹18.
Total contribution = 18 × 10,000 = ₹1,80,000.
Profit = Contribution − Fixed cost = 1,80,000 − 1,80,000 = ₹0.

Answer: Contribution per unit is ₹18, total contribution is ₹1,80,000 and profit is nil, because contribution exactly covers fixed cost.

Example 2

A firm produced 8,000 units and sold 6,000 units at ₹40 per unit. Variable cost is ₹24 per unit. Fixed cost is ₹60,000. There was no opening stock. Find profit and closing stock value under marginal costing. Also state what the closing stock value would be if fixed cost were absorbed on production.

Show the solution

Contribution per unit = 40 − 24 = ₹16.
Total contribution = 16 × 6,000 = ₹96,000.
Profit = 96,000 − 60,000 = ₹36,000.
Closing stock = 8,000 − 6,000 = 2,000 units.
Closing stock under marginal costing = 2,000 × 24 = ₹48,000.
For comparison, fixed cost per unit on production = 60,000 ÷ 8,000 = ₹7.50.
Absorption cost per unit = 24 + 7.50 = ₹31.50, so stock would be 2,000 × 31.50 = ₹63,000.

Answer: Profit under marginal costing is ₹36,000 and closing stock is ₹48,000. Under absorption costing the stock would be ₹63,000, because it carries ₹15,000 of fixed cost.

Exam tips

In a theory question on advantages and limitations, give 4 to 6 points each with a one-line reason. Balanced answers score better.
In numericals, always show the contribution statement line by line. Step marks are given even if one figure is wrong.
Check whether the question gives units produced and units sold separately. Stock valuation questions depend on this.
Read for hidden variable costs such as sales commission or packing. Missing them changes contribution.
MCQs on this topic often test definitions: contribution, fixed cost behaviour and stock valuation. Revise these in one sitting.

Practice questions from Marginal Costing

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 the difference between marginal cost and variable cost?

Marginal cost is the extra cost of producing one more unit. In exam problems it is taken as the variable cost per unit, so the two are used interchangeably. The theoretical idea of marginal cost is slightly wider because it is about the change in total cost.

Why is fixed cost not included in product cost under marginal costing?

Fixed cost does not change with output in the short run. It is incurred for the period, so marginal costing writes it off in that period. This avoids profit changing just because stock levels changed.

What are the main limitations of marginal costing?

Separating costs into fixed and variable is difficult, as many costs are semi-variable. Stock valued at variable cost only may not be accepted for external reporting. It also ignores that fixed cost is a real cost needing recovery in the long run, and it works best in the short run.

Is contribution the same as gross profit?

No. Contribution is sales minus variable cost, while gross profit is sales minus the full cost of goods sold, which includes fixed production overheads. The two figures usually differ.