Case Interview Examples: 3 Fully Worked Cases

Here are three case interview examples worked end to end: a profitability case, a market sizing case, and a market entry case. For each one you get the candidate's opening synthesis, the structure, the back-and-forth with the interviewer, the actual math, and a top-down recommendation. These are short cases meant to show the moves, not exhaust every branch. Read them as a choreography you can copy.

I ran more than 100 case interviews at McKinsey, and the single best way to learn the case is to watch one done well and steal the rhythm. New to the format? Start with what is a case interview for the ground rules, then come back here for the worked mechanics.

Before the cases, here is the shared rhythm every one of them follows. The interview is a dance with predictable steps.

Example 1: A profitability case

The prompt. "Our client is SnackCo, a packaged snack manufacturer with 500 million dollars in revenue. Over the past two years their profit has fallen by 30 percent even though sales are growing. They want to know why and how to fix it."

The opening. The candidate synthesizes rather than parrots: "So our client SnackCo is a 500 million dollar snack maker whose profit has dropped 30 percent over two years, and the puzzle is that this is happening while sales are actually growing. They want us to find the cause and reverse it. Is profit, specifically accounting profit, the right measure, and is reversing the decline the only goal?" The interviewer confirms yes. Notice the candidate flagged the tension immediately: profit down while sales up almost always means costs are rising faster than revenue.

The framework. "Profit equals Revenue minus Cost. Since revenue is rising, I'd like to first confirm revenue is genuinely up in dollars, then focus on the cost side, splitting it into fixed and variable, because that's where the problem most likely sits." Clean, built from an equation, and already pointing at the likely culprit. For the full method behind this, see my profitability case interview walkthrough.

The back-and-forth and math. Revenue grew from 450 million to 500 million dollars. Profit fell from 50 million to 35 million dollars, a drop of 15 million, which is the 30 percent. So cost rose from 400 million to 465 million, up 65 million dollars. The candidate splits cost. Fixed costs went from 100 million to 105 million, roughly flat. Variable costs went from 300 million to 360 million, up 60 million. Volume grew 15 percent, so some variable increase is expected, but the candidate checks variable cost per unit. Units went from 300 million to 345 million packs. Variable cost per pack went from 1.00 dollar to about 1.04 dollars, up 4 cents. The driver is a per-unit variable cost increase, traced to a more expensive new packaging material rolled out two years ago. The candidate marks 60 million as the key number.

The recommendation, delivered top-down. "Our recommendation is to roll back or renegotiate the new packaging, because it raised variable cost per pack by 4 cents and drove roughly 60 million dollars of the cost increase, which more than wipes out the profit from higher volume. Two reasons: the cost increase is structural and recurring, and volume growth is healthy, so the business is sound apart from this one input. Risks to consider: the new packaging may have shelf-life or branding benefits we should value before reverting, and suppliers may resist renegotiation." Then the candidate stops. No rambling, no recap.

Example 2: A market sizing case

The prompt. "How many gas stations are there in the United States?"

The opening. Sizing questions do not need a long synthesis, but they do need a stated approach. "I'll size this bottom-up, starting from the number of cars and how much fuel they need, then work out how many stations are required to serve them. Let me lay out my assumptions and you can correct any." That sentence buys you permission to assume, which is the whole point of sizing. My full method is in the market sizing case interview guide.

The structure and math. The candidate works in clean, round numbers and says each one aloud.

• US population: about 330 million people.
• Cars: assume roughly 1 car for every 2 people, so about 165 million cars. Round to 160 million.
• Fuel use: each car fills up, say, once a week, so about 50 fill-ups a year. That gives 160 million times 50, which is 8 billion fill-ups a year.
• Station capacity: a typical station has maybe 8 pumps, each serving roughly 4 cars an hour, open about 12 hours a day. That is 8 times 4 times 12, which is roughly 384 fill-ups a day, call it 400. Over 360 days, about 144 thousand fill-ups per station per year. Round to 150 thousand.
• Stations needed: 8 billion fill-ups divided by 150 thousand per station is about 53 thousand.

But the candidate sanity-checks, because pumps are not full all day. "Real stations run well below capacity, so the true number is higher than my capacity math suggests. Adjusting for maybe 40 percent utilization, I'd estimate somewhere around 120 to 150 thousand gas stations." That range brackets the real figure, which is around 145 thousand. The grade is not in hitting the number exactly. It is in the clean assumptions, the round arithmetic, and the sanity check.

The recommendation. Even a sizing gets a crisp close: "So my estimate is roughly 120 to 150 thousand gas stations in the US. The biggest swing factor is station utilization, so if we needed precision, that's the assumption I'd validate first." Lead with the number, name the sensitivity, stop.

A note on what just happened, because it is the most common place candidates lose points. The candidate never apologized for not knowing the real figure, never spiraled when the capacity math came out low, and never buried the interviewer in extra decimals. They picked round numbers on purpose so the arithmetic stayed clean, said every assumption out loud so the interviewer could redirect them, and ended with a range plus the one assumption that drives it. That is what a market sizing case is actually testing: comfort with ambiguity and structured estimation, not trivia. If your bottom-up and top-down approaches land in the same ballpark, even better, because agreement between two independent paths is strong evidence your estimate is sound.

Example 3: A market entry case

The prompt. "Our client is a successful US meal-kit company. They are considering entering the Brazilian market. Should they?"

The opening. "So our client is a profitable US meal-kit business weighing entry into Brazil, and they want a go or no-go. I'll structure this in four parts: is the Brazilian meal-kit market attractive, would entry be profitable for them, do they have a right to win there, and if so, how should they enter. Is maximizing long-term profit the goal?" Confirmed. The candidate has laid out the four steps cleanly. The full structure is in my market entry case interview guide.

The back-and-forth and math. Attractiveness first. Brazil has about 210 million people. Assume 30 percent are urban middle class likely to buy meal kits, about 60 million people, or roughly 20 million households. If 2 percent ever adopt meal kits, that is 400 thousand households, spending perhaps 1,000 dollars a year, a market of 400 million dollars. Decent size, and growing with urbanization. On five forces, barriers to entry are low and a few local players already exist, so rivalry will build.

Economics. The client thinks they can take 10 percent of that market in five years, which is 40 million dollars in revenue, against an upfront investment of 50 million dollars to build local sourcing and delivery, with maybe 8 million dollars in mature annual profit. Break-even is 50 divided by 8, which is over 6 years. Slow.

Right to win. This is the deciding step. Meal kits depend on local fresh-food supply chains and last-mile delivery, and the client has none of that in Brazil. Their US brand means little there, and Brazilian cuisine and grocery habits differ sharply from US ones, so their recipes and sourcing do not transfer. Their right to win is weak.

The recommendation, top-down. "Our recommendation is that the client should not enter Brazil directly at this time. Two reasons: their right to win is weak, because meal kits depend on local supply chains and delivery they don't have and a brand that doesn't carry over, and the economics are marginal, with a break-even beyond six years on a 50 million dollar bet. If they still want exposure to the market, the lower-risk path is a partnership or acquisition of an existing Brazilian player rather than building from scratch. The main risk to revisit is that a local partner could change this calculus quickly, so I'd validate partnership options before a final no." Clear, decisive, conditional where it should be.

The bottom line

Every case follows the same four-beat dance: open by synthesizing and confirming the goal, structure from an equation or a clean breakdown, do the math in round numbers with a sanity check, and close top-down with a recommendation, two or three reasons, and the risks. The case type changes the framework, but the rhythm never changes. Learn the rhythm and any case becomes recognizable.

Go deeper

These three are a taste of the dozens of fully worked cases inside Cut to the Case, where the Interview Dance method turns this rhythm into muscle memory and the CaseMap system gives you the business concepts to fill any framework.

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