4.1Cost accounting & cost calculation
The essentials in 30 seconds
- Central question: general accounting says how much we earn globally; cost accounting says where we make or lose money (by product, service, activity, customer).
- Three methods by decision: full cost to set a price covering everything, variable cost to reason in margin (short term), marginal cost to accept one more unit or not.
- Central difficulty: allocating indirect costs (rent, administration) via keys or the ABC method — the chosen key strongly influences the result.
Running mini-case — Rachid and the star product that loses money
Rachid runs a small business selling several products in Algiers. Turnover grows and the overall result stays profitable, but cash tightens. Calculating full costs per product for the first time, he discovers his star product — the best seller — is sold at a loss, while a discreet product earns a strong margin. We follow his investigation, from the method choice to the decision.
This same case returns in the lesson, the diagram, the script and the 48h challenge — and continues in 4.2, 4.3, 4.4 and 4.5.
1. Where do we make money?
General accounting says how much the business earns globally; cost accounting (management accounting) answers “where do we make or lose money?”. Rachid lives it: his overall result hid a loss-making product.
Its core is the calculation of costs: what a product, a service, an activity, a customer really costs — to know its profitability and decide. Without it, you fight for unprofitable turnover: selling a lot is not earning money.
2. Three methods by question asked
The full cost (all charges, direct and indirect) sets a price covering everything. The variable cost (direct costing, variable charges only) reasons in contribution margin for short-term decisions. The marginal cost (cost of one additional unit) accepts or refuses one more order.
Rachid keeps the reflex: choose the method by the question — set a price, judge a profitability, decide one more order — not the reverse.
3. The crux: indirect costs
The recurring challenge is allocating indirect costs (rent, administration) that cannot be attached directly to a product — via allocation keys or the ABC method (costs by activity, attaching charges via activities actually consumed).
Cost accounting is free and tailor-made: the tool for fine steering and informed decisions — provided you stay aware that the chosen key influences the result.
🔎 Concrete example — The loss-making star product (Rachid's case)
Rachid finally calculates the full costs of his two products.
Star product: sells very well but, full costs calculated, sold at a loss.
Discreet product: modest volumes but strong margin.
→ without cost calculation, Rachid fought for unprofitable turnover.Result: know each product's real profitability before setting prices and efforts.
Reflex: choose the method by the question asked (price, margin, additional order).
Section vocabulary
- Cost accounting
- Management accounting calculating costs and margins per product, activity or customer to inform decisions.
Simple example: Rachid calculates each product's cost instead of watching the overall result only.
What it is not: general accounting, which only says how much the business earns globally.
Reflex: facing an overall result, ask “where, exactly, do we make or lose?”.
- Full cost
- Sum of all charges (direct and indirect) attached to a product; basis for a price covering everything.
Simple example: Rachid adds direct charges and an indirect share for his star product.
What it is not: a price set by feel, never checked against all charges.
Reflex: before setting a price, check it covers the full cost.
- Variable cost (direct costing)
- Cost keeping only variable charges, to reason in contribution margin (short-term decisions).
Simple example: Rachid judges a short-term decision on the margin left after variable charges.
What it is not: using full cost for a very short-term decision.
Reflex: for the short term, reason in contribution margin.
- Marginal cost
- Cost of producing one additional unit; useful to accept an extra order or not.
Simple example: Rachid accepts one more order only if its marginal cost is covered.
What it is not: redoing the whole full calculation for each additional unit.
Reflex: one more order = look at the cost of one more unit.
- Indirect costs
- Charges not directly attachable to a product (rent, administration), to allocate via keys or ABC.
Simple example: Rachid's rent split between products via a key — or via activities (ABC).
What it is not: charges forgotten and never attached, falsifying every cost.
Reflex: always state the chosen key and its effect on the result.
In practice — Calculating and using costs (Rachid's case)
- Name your question: set a price, judge a product's profitability, decide one more order?
- Choose the adapted method: full (price), variable (margin, short term), marginal (additional unit).
- Split direct charges (attachable) and indirect (to allocate via an explicit key or ABC).
- Calculate the margin per product or activity and decide: price, sales effort, drop or keep.
Ready-to-say script — explain the loss-making product (1 min)
“Our star product sells well, but full costs calculated, it is sold at a loss: the overall result hid its negative margin. The discreet product earns a real margin. I propose reviewing the first one's price and pushing the second — and choosing the costing method by each decision from now on.”
To say in a meeting: overall result, profitability per product, proposed decision — no jargon.
Copy-paste template — cost sheet per product
PRODUCT / ACTIVITY: _______________
QUESTION ASKED: _______________
CHOSEN METHOD (full / variable / marginal): _______________
DIRECT CHARGES: _______________
INDIRECT CHARGES + KEY USED: _______________
MARGIN PER PRODUCT: _______________
DECISION (price / effort / drop): _______________Small business / low volume
Few products: a one-page sheet per product is enough — the point is splitting direct and indirect.
SME Algiers
Charges shared between activities (premises, transport, administration): state the local key used to avoid misunderstandings.
Service / freelance
Apply the reasoning to assignments: time spent (direct) + share of fixed costs (indirect) per job.
Management beginner
Start with one doubtful product (the “star”) before generalising to the whole range.
✓ Best practices
- Choose the costing method by the decision to make, not by habit.
- Stay aware that the allocation key strongly influences the result.
- Hunt the loss-making products hidden by star products.
✗ Common pitfalls
- Confusing “we sell a lot” and “we make money”.
- Choosing an arbitrary allocation key and falsifying apparent profitability.
- Selling at a loss without knowing it, for lack of knowing your costs.
Key takeaways
- Cost accounting answers “where do we make or lose money?” via cost calculation.
- Methods: full cost (set a price), variable cost (short-term decisions), marginal cost (additional unit).
- Central difficulty: allocating indirect costs (allocation keys, ABC method).
- It is free and tailor-made; the tool for fine steering and informed decisions.
48h challenge — apply tomorrow
Take 1 product or 1 activity (Rachid's “star”), list its direct and indirect charges with the key used, and calculate its margin. Note the decision that figure suggests.
- I can name the 3 methods and their right use.
- I can explain why the allocation key changes the result.
- I have calculated (or scheduled) the margin of 1 real product.
Frequently asked questions
Why is cost calculation so important for decisions?
Because without it, you decide blind: a well-selling product can be loss-making (sold too low, badly costed), while a discreet product can be very profitable. Knowing each product, service or customer's real cost lets you set a price covering costs, stop or review an unprofitable product and focus efforts on what pays. The difference between “we sell a lot” and “we make money”.
Why is allocating indirect costs so tricky?
Because indirect costs (rent, electricity, administration) cannot be attached naturally to a product: they must be allocated by keys, and each key gives a different cost, hence a different apparent profitability. A bad key makes an unprofitable product look profitable (or the reverse). Finer methods like ABC attach charges via activities actually consumed. No “perfect” allocation exists: hence choosing relevant keys and staying aware matters.
Rachid sells a lot but cash tightens: his star product may be sold at a loss. Which question does cost accounting answer first?