Marginal Costing

🟢 Lite — Quick Review (1h–1d)

Rapid summary for last-minute revision before your exam.

Marginal Costing charges only variable costs to a product; fixed costs are written off in full against the contribution of the period in which they arise. The marginal cost of one unit equals its variable cost.

Contribution = Sales − Variable Cost. It is the fund that pays off fixed cost and then becomes profit. P/V Ratio = Contribution ÷ Sales × 100, expressing how much each rupee of sales contributes. Break-even Point (units) = Fixed Cost ÷ Contribution per unit. Margin of Safety = Actual Sales − Break-even Sales — the buffer before a loss appears.

For CMA Foundation, expect short numericals on BEP, P/V ratio and MoS, plus one theory item on why fixed cost is treated as a period cost. Always split semi-variable costs into fixed and variable elements before applying formulas.

🟡 Standard — Regular Study (2d–2mo)

Standard content for students with a few days to months.

Core Logic of Marginal Costing

Under absorption costing every cost — fixed or variable — is absorbed into the product. Marginal costing deliberately excludes fixed overhead from product cost and treats it as a period cost charged fully in the income statement of that period. This makes profit move in step with sales volume, which is the analytical strength of the technique. Closing stock is therefore valued at variable cost only.

Contribution and P/V Ratio

Contribution per unit = Selling price − Variable cost per unit. Aggregated, Total Contribution = Sales − Total Variable Cost. The P/V Ratio (Contribution/Sales × 100) measures the rate at which contribution is generated. A higher P/V ratio means fewer additional sales rupees are needed to recover fixed cost. Two products can be compared by contribution per rupee of a scarce resource using the formula:

Contribution per unit of Key Factor = Contribution per unit ÷ units of key factor consumed.

Break-Even and Margin of Safety

The break-even point is the sales volume at which total contribution equals fixed cost (profit = 0). In units: BEP = Fixed Cost ÷ Contribution per unit. In rupees: BEP = Fixed Cost ÷ P/V Ratio. The Margin of Safety = Budgeted (or actual) sales − BEP sales; expressed as a percentage of actual sales it tells management how much sales can drop before a loss sets in.

Target Profit and Decision Use

To earn a target profit, Required Sales (₹) = (Fixed Cost + Target Profit) ÷ P/V Ratio. Marginal costing underpins short-term decisions — make-or-buy, accepting a special order at lower price, dropping or adding a product line, and choosing the optimum sales mix when a key factor is limiting output.

Exam Pattern (CMA Foundation Accounting, ~3% weight)

Questions are typically 4–8 marks numericals on BEP, P/V ratio, MoS and multi-product break-even, plus a 2-mark concept question. Carry figures to two decimals and present the formula before substitution to earn method marks.

🔴 Extended — Deep Study (3mo+)

Comprehensive coverage for students on a longer study timeline.

Cost Behaviour and the Relevant Range

The distinction between fixed and variable rests on behaviour within a relevant range of activity. Fixed costs stay constant in total but vary per unit; variable costs stay constant per unit but vary in total. Outside the relevant range fixed costs step up (e.g., a new supervisor, an additional factory shift), so break-even charts must be drawn for the band currently applicable. Step costs and semi-variable costs must be decomposed — using the high–low method or regression — before any CVP calculation, otherwise P/V ratio and BEP become unreliable.

Multi-Product Break-Even

When a firm sells several products, a composite P/V ratio is computed as weighted average contribution ÷ weighted average sales, using the sales-mix proportions as weights. The composite BEP in rupees = Total Fixed Cost ÷ Composite P/V Ratio. Individual product BEPs are then derived using the mix ratio. A change in mix alters the composite ratio even if nothing else changes — a frequently tested trap.

Worked Micro-Example

A unit sells for ₹100, variable cost ₹60, so contribution per unit = ₹40 and P/V ratio = 40%. Fixed cost = ₹2,00,000. BEP (units) = 2,00,000 ÷ 40 = 5,000 units, equalling ₹5,00,000 in sales. Budgeted sales are 7,000 units (₹7,00,000), so Margin of Safety = 2,000 units or ₹2,00,000 (28.57% of actual sales). To earn a target profit of ₹80,000: Required sales = (2,00,000 + 80,000) ÷ 0.40 = ₹7,00,000 (7,000 units) — the entire budgeted volume.

Edge Cases and Common Mistakes

Treating semi-variable cost as wholly fixed or wholly variable biases the P/V ratio.
Confusing contribution with gross profit; gross profit still carries an allocation of fixed overhead.
Valuing closing stock at marginal cost under marginal costing but at full cost under absorption costing — the difference reconciles the two profits.
Using book value or sunk cost in a make-or-buy analysis; only future avoidable costs are relevant, and the offer price is compared with variable cost of making plus any avoidable fixed cost.
Forgetting that BEP assumptions (linearity, constant mix, single product or fixed mix, no inventory change) rarely hold perfectly in practice.

Practice Prompts

From the following — selling price ₹50, variable cost ₹30, fixed cost ₹60,000 — compute BEP in units and rupees, P/V ratio, and Margin of Safety when actual sales are 4,000 units.
Two products A and B sell in a 3 : 2 mix. Contribution per unit: A = ₹20, B = ₹15. Selling prices: A = ₹50, B = ₹40. Fixed cost ₹1,70,000. Compute the composite P/V ratio, overall break-even sales, and break-even units of each product.

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Marginal Costing