Case Interview Prep: McKinsey, BCG & Bain Guide

Consulting case interviews are unlike any other interview format. They're live business problem-solving sessions where you're expected to structure ambiguous problems, perform mental math, and deliver actionable recommendations — all in 30-40 minutes. At McKinsey, BCG, and Bain (MBB), the case interview is the primary hiring filter, and even brilliant candidates fail without proper preparation. This guide covers every framework, technique, and practice strategy you need to crack consulting case interviews.

How Case Interviews Work (Structure & Format)

A typical consulting interview loop includes 2-3 rounds with 2 cases per round (4-6 cases total). Each case follows a consistent structure:

1. Problem statement (1-2 minutes) — The interviewer presents a business scenario.
2. Clarifying questions (1-2 minutes) — You ask smart questions to narrow scope.
3. Structure (3-4 minutes) — You take a moment to build your framework, then present it. This is the most critical phase.
4. Analysis (15-20 minutes) — You work through your framework with the interviewer, who provides data as you ask for it.
5. Recommendation (2-3 minutes) — You synthesize your findings into a clear, actionable recommendation.

MBB-Specific Differences

• McKinsey — Uses "interviewer-led" cases. Also includes the McKinsey Problem-Solving Game (Imbellus) as a digital assessment.
• BCG — Cases tend to be more "candidate-led" with open-ended exploration. BCG also uses the BCG Casey chatbot test.
• Bain — Similar to BCG's format but often includes a written case or group case in final rounds. Bain cases frequently involve private equity scenarios.

The 7 Classic Case Frameworks

Frameworks are starting structures, not rigid templates. Mastering these seven gives you building blocks for any case:

Critical tip: Never say the name of a textbook framework out loud. Instead, present your structure as custom-built: "I'd break this into two key areas: first, understanding what's happening on the revenue side, and second, examining the cost structure."

Market Sizing Questions: Step-by-Step Method

The Approach

1. Clarify scope — Geography, time period, definition (revenue or units?)
2. Choose your method — Top-down (population, filter down) or bottom-up (single unit, scale up)
3. State your assumptions explicitly — Reasonable assumptions matter more than the final number
4. Do the math cleanly — Round aggressively, use round numbers
5. Sanity check — Compare to something known

Worked Example: "How many cups of coffee are sold daily in the US?"

Step 1 — Scope: US only, all coffee, daily volume.

Step 2 — Top-down: US population: ~330 million. Adults (18+): ~75% = 250 million. Coffee drinkers: ~65% = ~160 million. Average cups per drinker per day: ~2. Total: 160M x 2 = ~320 million cups per day

Step 3 — Sanity check: The National Coffee Association reports about 400 million cups daily. Our estimate of 320 million is within 20%, which is strong for an interview setting.

Profitability Cases: Revenue vs Cost Analysis

Profitability is the single most common case type, appearing in roughly 30-40% of all consulting interviews.

Revenue Deep Dive

• Revenue = Price x Volume
• Segment by product line, customer segment, geography, or channel
• Compare current period to historical baseline — which segment changed?

Cost Deep Dive

• Fixed costs: Rent, salaries, depreciation, insurance
• Variable costs: Raw materials, shipping, commissions
• Benchmark against industry averages

M&A and Market Entry Scenarios

Market Entry Framework

1. Market attractiveness — Size, growth rate, margins, Porter's Five Forces
2. Competitive landscape — Incumbents, market share, differentiation
3. Client capabilities — Skills, distribution, brand, technology gaps
4. Financial analysis — Required investment, break-even, ROI

M&A Framework

• Standalone value of the target — Revenue growth, profitability, competitive position
• Synergies — Revenue synergies and cost synergies. Be skeptical — most acquirers overestimate synergies.
• Integration risks — Culture clash, technology compatibility, key employee retention
• Valuation — DCF, comparable transactions, and public market multiples

Mental Math Tips for Case Interviews

• Round aggressively — 4.8 million is 5 million. 37% is "roughly 40%."
• Break multiplication into parts — 43 x 17 = (40 x 17) + (3 x 17) = 680 + 51 = 731
• Memorize key benchmarks — US population (330M), world population (8B), US GDP ($28T)
• The Rule of 72 — Divide 72 by the growth rate to estimate doubling time
• Percentage shortcuts — 15% = 10% + 5% (half of 10%)

Practice Plan: 4-Week Case Prep Roadmap

By the end of four weeks, you'll have completed 20-26 practice cases. Research shows that candidates who practice 30+ cases have a significantly higher success rate at MBB firms.

Conclusion

Case interviews are a learnable skill, not an innate talent. Master the frameworks, practice your mental math daily, and invest heavily in partner practice with honest feedback. Pair your case prep with strong behavioral interview stories and regular mock interview sessions to build the confidence and polish that interviewers look for.

Ready to practice with real-time AI feedback? Try InterviewAlly free and sharpen your problem-solving, communication, and analytical skills with instant AI-powered coaching.