Intuition
Money words trip people up because they sound interchangeable but aren't. "Margin," "profit," "cost" — interviewers use them precisely, and using them loosely is an instant tell that you don't think in numbers. The good news: there are only a handful of terms, and they fit together like a set of nesting bowls. Once you can see how revenue gets whittled down to net profit, the whole vocabulary clicks.
Picture a paycheck. Your gross pay is revenue. After the unavoidable deductions you get take-home — that's your margin. Costs are everything pulling the two apart.
Framework
- Profit = Revenue − Costs. The foundation of every profitability case.
- Gross margin = (Revenue − COGS) / Revenue. Measures how profitable each sale is before overhead.
- Net margin = Net profit / Revenue. After all costs — operating, interest, tax. The bottom line.
- Fixed costs don't move with volume (rent, salaried staff). Variable costs scale per unit (materials, commissions, shipping).
- Contribution margin = price − variable cost per unit. What each extra sale contributes toward covering fixed costs.
Worked Example
A bakery sells bread at $4. Flour, energy, and packaging cost $1.50 per loaf (variable); rent and salaries are $6,000/month (fixed). Contribution margin = $4 − $1.50 = $2.50 per loaf. To break even it must sell $6,000 / $2.50 = 2,400 loaves a month. If a competitor forces the price to $3, contribution drops to $1.50 and break-even jumps to 4,000 loaves — same fixed cost, far more volume needed. That single split explains why the price cut is dangerous.
Pitfalls
- Confusing margin (a percentage or per-unit figure) with profit (an absolute dollar amount).
- Assuming all costs can be cut equally — fixed costs are sticky in the short run.
- Forgetting that a margin can shrink even as revenue grows, if costs grow faster.