In plain English
Financial accounting tells outsiders how the whole company did. Management accounting tells insiders which product, customer or factory made the money. It is the lens for almost every cost-cutting and pricing project a consultant runs.
The advanced view
The central problem is joint cost: overheads are consumed by activities, not by revenue, so any allocation based on volume systematically cross-subsidises low-volume complexity with high-volume simplicity. Activity-based costing re-attributes cost to the drivers that actually cause it, which typically reveals that a minority of products and customers generate all the profit and the rest destroy it.
Start with the fixed/variable split, because every operational decision hinges on it. Contribution margin — price minus variable cost — is what each extra unit contributes to covering fixed cost. Once fixed costs are covered, contribution falls straight to profit, which is why operating leverage magnifies both directions: a business with high fixed cost turns a 10% volume swing into a much larger profit swing.
Cost and variance arithmetic
Contribution margin = Price − Variable cost per unit Break-even volume = Fixed costs / Contribution margin Break-even revenue = Fixed costs / Contribution margin % Degree of operating leverage = Contribution / Operating profit = %Δprofit / %Δvolume Price variance = (Actual price − Budget price) × Actual volume Volume variance = (Actual volume − Budget volume) × Budget contribution Mix variance = Σ (Actual mix % − Budget mix %) × Actual total volume × Budget contribution per unit ABC rate = Activity cost pool / Total cost-driver units
Worked example: price/volume/mix bridge
Step 1 of 9
- 1Budget: 1,000 units at 100 → revenue 100,000; actual: 1,100 units at 96 → revenue 105,600
Activity-based costing replaces one plant-wide overhead rate with a rate per activity: setups, orders processed, deliveries, engineering changes, invoices. Cost is traced to the activity, then to the product or customer that consumes it. The result is usually a whale curve — cumulative profit rises to a peak well above 100% of reported profit and then falls back, because a tail of small, complex, high-service customers costs more to serve than they pay. That chart is the starting point for pricing, service-level and rationalisation decisions.
The consultant's cost toolkit
Cost-to-serve
Full cost of serving each customer including order handling, delivery frequency, returns and support. Reveals the profit tail.
Zero-based budgeting
Rebuild the cost base from zero each cycle rather than growing last year's. Effective once, hard to repeat annually.
Should-cost analysis
Model what a component ought to cost from materials, labour and margin, then negotiate against it.
Transfer pricing
The internal price between divisions. Market price where a market exists, otherwise marginal cost plus a share of contribution; drives both behaviour and tax.
Standard costing and variances
Compare actuals to a standard and decompose the gap into price, volume, mix, efficiency and spend.
Make versus buy
Compare avoidable cost, not fully allocated cost, to the external price; add capacity, quality and dependency effects.
Must know cold
- ✓Break-even = fixed cost / contribution margin per unit.
- ✓Only avoidable costs matter in a make-or-buy or shutdown decision; allocated overhead usually is not avoidable.
- ✓Price, volume and mix must reconcile exactly to the revenue or contribution bridge.
- ✓High operating leverage means high profit sensitivity in both directions.
- ✓ABC changes reported product profitability without changing a single krona of total cost.
- ✓A transfer price that beats a division's own economics will be gamed; expect the behaviour it pays for.
Common pitfalls
- ×Allocating overhead on revenue, which makes the biggest product look the most expensive.
- ×Cutting a product that carries allocated overhead the rest of the portfolio then has to absorb.
- ×Confusing gross margin with contribution margin when some COGS is fixed.
- ×Building a price/volume/mix bridge whose effects do not sum to the actual variance.
- ×Treating a step-fixed cost — a second shift, another line — as linear.
Essential vocabulary
- Contribution margin
- Revenue minus variable cost; what each unit contributes toward fixed costs and profit.
- Cost driver
- The activity measure that causes a cost pool to change — setups, orders, deliveries.
- Whale curve
- Cumulative profit by customer, peaking above 100% before the loss-making tail pulls it down.
- Step cost
- A cost that is fixed within a capacity band and jumps at the boundary.
- Avoidable cost
- Cost that genuinely disappears if the activity stops; the only cost relevant to the decision.
Strategy connection
Cost leadership is not a slogan, it is a cost structure. Knowing which costs are variable, which are step-fixed and which are truly fixed tells you the volume at which you win a price war and the volume at which you lose it — the same arithmetic underpins capacity, outsourcing and footprint decisions.
Exercises
Try each one on paper before revealing the worked solution.
Exercise 1
Fixed costs are 4.5m, price 120, variable cost 75. Find break-even volume, and the volume needed for 1.8m of operating profit. Then compute the degree of operating leverage at that point.
Exercise 2
A plant allocates 6m of overhead across two products on labour hours: Standard uses 90,000 hours for 300,000 units, Custom 30,000 hours for 20,000 units. ABC finds overhead is driven by setups: 200 setups for Standard, 1,800 for Custom. Compare unit overhead.
Exercise 3
Structuring exercise: a manufacturer's margin fell 3pp while revenue grew 8%. Structure the diagnosis before touching data.
Revenue rises with volume from zero; total cost starts at the fixed base. They cross at break-even = fixed cost / contribution margin per unit. The steeper the gap after that point, the higher the operating leverage — great in an upturn, brutal in a downturn.