Case Interview Preparation — How to Pass McKinsey, BCG, and Bain

The core of case interview success is mastering 4-5 foundational frameworks that allow you to structure nearly any problem you encounter. The most essential is the 2x2 framework — when asked about profitability or growth, split the problem into two independent dimensions. For profitability: Revenue (volume × price) and Costs (fixed + variable). For growth: existing customers (retention × usage) and new customers (market size × penetration). This isn't about memorising the framework; it's about recognising that complex problems become manageable when decomposed.

The second critical framework is the Five Forces analysis for competitive positioning — threat of new entrants, bargaining power of suppliers, bargaining power of customers, threat of substitutes, and competitive rivalry. This framework helps you think systematically about why a market is attractive or unattractive. Don't recite the framework; use it as a thinking tool. Ask "Does this problem involve competitive dynamics? If so, what forces matter most?"

Market sizing — estimating the size of a market you've never studied — is central to many cases. The method is simple: break the market into addressable segments, estimate the size of each, and sum. For "What is the UK market for high-end coffee?" break it down to: UK population × % who drink coffee regularly × % who buy premium coffee × annual spend. Do the maths aloud, reason through your assumptions, and acknowledge uncertainty. Interviewers don't expect accuracy; they expect logical thinking.

Other essential frameworks include the growth-share matrix (assessing a portfolio of products or businesses), cost structure analysis (understanding where profit leaks), and customer journey analysis (identifying where value is created or lost). Learn these frameworks deeply enough that you can apply them without consciously thinking about them. The best case candidates don't reference frameworks explicitly — they use them intuitively.

The most common mistake is poor listening. Candidates hear the initial case statement and immediately start talking about what they think matters, without asking clarifying questions. Listen intently, take notes, and ask at least 2-3 clarifying questions before outlining your approach. "How are we defining success? Is this about market share, profitability, or something else? And what is our current position in this market?" These questions accomplish two things: they help you think better, and they signal to the interviewer that you engage carefully with problems.

The second mistake is pursuing irrelevant detail. You have 30-40 minutes. If you spend 10 minutes analysing corporate culture when the case is about market entry, you've wasted time. The interviewer will try to redirect you with hints. If they say "That's interesting, but maybe less important for this decision — let's focus on the financial side," take that feedback immediately. Many candidates feel compelled to finish their thought. Don't. Redirect gracefully: "Good point. Let me focus on the financial analysis."

The third mistake is doing maths wrong or doing it too slowly. You don't need a calculator. Brush up on mental arithmetic — multiply two-digit numbers, divide by fractions, and convert percentages to actual figures. Practice estimation under time pressure. If you stumble on basic maths, write it down: "Let me make sure I've got this right — £500m × 0.15 × 0.12 = £9m." Taking 10 seconds to get the right answer is better than confidently stating a wrong figure.

Finally, don't memorise case answers. Interviewers ask different questions, and memorised responses sound robotic. Instead, internalise the frameworks and practise the thinking process. Each case should feel like a conversation where you're thinking alongside the interviewer, not a recitation of a prepared solution.