Consulting case interview: structure and a market sizing walk-through
A case interview tests how you break a messy problem down and communicate it. You do not need to know the answer, you need a clear route to one.
Sample candidate (fictional): Rohan, a final-year MBA student working through a practice case with a friend. Every example answer is invented for practice. Rewrite them with your own facts.
Worked example: how many coffees does a mid-size city drink in a day?
Every number below is an assumption chosen for practice, and is not data. The interviewer cares about your structure and whether your assumptions are sensible and clearly stated.
Rohan says out loud: "I will split the city by who drinks coffee, then estimate cups per person, and sanity-check the total."
- Population: assume 2 million people in the city.
- Who drinks coffee: assume 40% are regular drinkers, so 800,000 people. Rohan notes that children and non-drinkers are excluded.
- Cups per day: split regular drinkers into light (1 cup, 70%) and heavy (3 cups, 30%). Average is 0.7 x 1 + 0.3 x 3 = 1.6 cups.
- Total: 800,000 x 1.6 = about 1.3 million cups a day.
- Sanity check: 1.3 million cups in a city of 2 million is 0.64 cups per person on average. That feels plausible for a place with a mixed tea and coffee habit.
- Say what would change it: tea-dominant cities lower the share, and tourist areas raise it. Offer to refine either.
Common questions
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How do I start a case?
How to answer
Repeat the question back, ask one or two clarifying questions, then take a moment to build a structure. Silence for thirty seconds is fine.
Example answer
So we are asking whether a regional bakery chain should open a new outlet. Can I check the goal, profit or market share, and the time frame? Thanks. I would like a minute to structure my thoughts.
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What is a good structure for a profitability case?
How to answer
Profit is revenue minus cost. Break revenue into volume and price, and cost into fixed and variable. Then ask where the change happened.
Example answer
Profit fell, so I would look at revenue and cost separately. For revenue: volume and price by product. For cost: fixed and variable. First, can I see whether profit fell because of revenue or cost, and over what period?
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How do I structure a market entry case?
How to answer
Cover market attractiveness, the company's ability to compete, the entry route and the financials. Pick the branches that matter and say why.
Example answer
I would look at four areas: how big and how attractive the market is, how we compare with existing players, how we might enter (build, buy, partner), and whether the numbers work. I would start with market size and growth.
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How do I do a market sizing estimate?
How to answer
Pick top-down or bottom-up, split into simple pieces, state each assumption, round numbers for easy maths, then sanity-check.
Example answer
I will go bottom-up: number of households, share that would buy, and spend per household each year. I will assume numbers I can defend and check the total against a known benchmark.
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What if I do not know a number?
How to answer
Say so, give a reasoned estimate, and say how you would verify it. Guessing silently is worse than asking.
Example answer
I do not know the exact population. I will assume about two million for a mid-size city, and if you have a figure I will update the model.
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How should I handle the maths?
How to answer
Write the numbers on paper, round when you can, and say the units. State the result in words, not just digits.
Example answer
800,000 people times 1.6 cups is roughly 1.3 million cups per day. Let me check units: people times cups per person gives cups.
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What do I do when the interviewer pushes back?
How to answer
Treat it as information, not an attack. Ask what they are seeing, adjust, and explain the change.
Example answer
That is a fair point. If the average customer buys less than I assumed, revenue falls and the break-even moves out. Let me redo that step with your number.
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How do I finish a case?
How to answer
Give a recommendation first, then two or three reasons, then risks and next steps. Keep it under a minute.
Example answer
I recommend opening the outlet. Reasons: the local market is growing, our margin per outlet is above break-even in the base case, and the lease is flexible. Main risk is footfall, so I would pilot for three months and review.
Practise it out loud
Say your answers to a mock question, then tighten them. Try it free in your browser, or build the resume the questions will come from.