In this article
Start here: the learning path
Learn the material in these five stages, because each step uses the one before it. Fit questions run alongside the whole path, not after it.
- Case interview
- A case interview is a structured conversation in which a candidate works through a realistic business problem with an interviewer, structuring the question, analysing data and reaching a recommendation, so that the interviewer can judge how the candidate reasons.
- Issue tree
- An issue tree is a diagram that breaks one business question into branches that are MECE (mutually exclusive, collectively exhaustive), each of which can be tested with data, so that the analysis covers the whole problem without overlap.
- Profitability case
- A profitability case is a case type that asks why a company's profit is falling or how to raise it, answered by splitting profit into revenue and cost, where revenue is volume times price and cost is fixed cost plus volume times unit cost.
Text description of the diagram
- Structure comes first and the synthesis comes last.
- Market sizing is the second stage, before case math.
- Structure. Build an issue tree and say it aloud.
- Market sizing. Estimate a market from drivers; start with the market sizing guide.
- Case math. Percentages, margins and break-even without a calculator.
- The case families. Profitability, market entry, mergers and acquisitions, and growth.
- Synthesis. Close with the answer first.
Alongside all five: fit and your story, meaning why consulting and your walk-through of your own experience.
- Market sizing: how to estimate a market in a case interview
- McKinsey PEI questions and how the Personal Experience Interview works
- Profitability case walkthrough, step by step
- Consulting case study practice: 20 original cases with model solutions
- Case interview frameworks that still work in 2026
- Case math drills: percentages, growth, CAGR and break-even
- M&A due-diligence case: how to solve one step by step
- What is the synthesis in a case interview, and how do you give one?
- What is a market entry case, and how do you solve one?
Why this order
Structure comes first because every case starts with an issue tree. Market sizing comes next because it trains the habit every other case needs: stating assumptions and checking them.
What case interviews test
Case interviews test how you reason through a problem. Boston Consulting Group (BCG) describes its case as a realistic business challenge and says "what matters most is how you approach the problem and the quality of your reasoning" (BCG careers, read October 2026). Its page lists what candidates do: structure an approach, ask thoughtful questions, analyse data, perform quick calculations and identify the most important factors. Bain describes such interviews as work where you "work through a problem" (Bain careers, read October 2026).
The case is one part of a loop. BCG lists a skills interview on experience and motivation, a case interview for client-facing roles, and a team interview that assesses problem-solving, analytical and communication skills (BCG interview process page, read October 2026). The work behind the interview is analytical consulting: the U.S. Bureau of Labor Statistics (BLS) says management analysts analyse financial and other data, develop solutions and present recommendations, and lists analytical, communication and problem-solving skills as key (BLS Occupational Outlook Handbook, last modified August 2026).
Knowing it is half the job. Saying it is the other half.
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Start Free Trial →A profitability case in numbers
A profitability case is solved by splitting profit into revenue minus cost, and testing each side in turn. The example below is illustrative: a made-up regional chain, with amounts in currency units and not in any real currency, chosen to show the method.1
Year 1: the chain sells 1,000,000 units at a price of 5.00, so revenue is 5.0 million. Cost is 3.20 per unit, or 3.2 million, plus 1.2 million of fixed cost, so profit is 0.6 million, a margin of 12.0%.1 Year 2: volume and price are unchanged, but cost per unit rises to 3.60. Cost is now 4.8 million and profit falls to 0.2 million, a margin of 4.0%. Profit is down 66.7% although unit cost rose by only 12.5%.1
The structure of the answer matters more than the arithmetic. Profit is revenue minus cost, revenue is volume times price, and cost is fixed cost plus volume times unit cost. Check volume, price, unit cost and fixed cost one at a time, find that only unit cost moved, then ask why. A recommendation follows from the numbers: to restore year-1 profit at the new cost, the price would have to rise from 5.00 to 5.40, which is 8.0%, so the next question is whether customers would accept that or whether the cost increase can be reversed.1
Text description of the diagram
- Profit is down 66.7% although unit cost rose by only 12.5%.
- Cost is now 4.8 million and profit falls to 0.2 million, a margin of 4.0%.
The topics in this path
Each topic below gets a short section, with a link where a full guide exists.
Market sizing
Market sizing is an estimate of how many units or how much revenue a market holds, built from drivers you can reason about and checked a second way. It is the cleanest drill for case thinking because every step is visible: define the unit, choose a route, build the tree, multiply and cross-check. Interviewers use it as a warm-up or as a full case. The Market sizing: how to estimate a market in a case interview page works a numeric example with two independent routes. The trap is to start multiplying before agreeing what "market" means. Say the definition aloud first, then give a range, not a single figure, and name the assumption you would test first.
The Personal Experience Interview
Some firms replace standard behavioral questions with a structured segment. Yale's career office describes the McKinsey Personal Experience Interview (PEI) as "a separate behavioral portion of the interview process", usually replacing standard behavioral questions (Yale Office of Career Strategy, read October 2026). The page McKinsey PEI questions: how the Personal Experience Interview works covers how to choose a story, how to tell it, and how to answer probing follow-ups about your own decisions. The trap is a story in which "we" did everything. Practise saying what you personally decided, what you weighed and what you would change, and read the behavioral interviews guide for the wider craft.
Profitability case walk-through
A profitability walk-through takes the case above and runs it as an interview: the opening question, the clarifying questions, the issue tree, the data requests and the recommendation. The structure splits profit into revenue and cost, revenue into volume and price, and cost into fixed and variable. In the illustrative case the data requests come in that order: volume, then price, then unit cost, then fixed cost, and only unit cost has moved. The case often has a twist, such as a mix shift or a one-off cost, and finding it is the skill being tested. The trap is jumping to a cause after the first data point. Ask for the next cut of the data before concluding.
Twenty practice cases with model solutions
A practice set is only useful if each case is solved out loud against a model answer, then re-solved. The page Consulting case study practice: 20 original cases with model solutions gives twenty original cases across the families, each with the question, the data the interviewer would hand out and a model solution that shows the structure, the numbers and the synthesis. The trap is reading solutions instead of solving. Cover the answer, speak your own structure, and only then compare. Track which family you drop points on, and drill that one next. Time each case and keep a short written note on what you would do differently.
Frameworks that still work
A framework is a reusable starting structure, such as revenue minus cost or customers, company, competitors and context. The page Case interview frameworks that still work in 2026 compares the common ones and shows when each breaks. The common failure is reciting a memorised framework that does not fit the question; interviewers notice, and BCG's own tips include, in its Do list, "Think Structurally" and, in its Don't list, "Overcomplicate Solutions" (BCG careers, read October 2026).
Use a framework as a prompt, then tailor the branches to the problem in front of you, and drop any branch that the question does not need. A good test is whether each branch could be answered with a number or a fact; if not, rewrite it.
Case math drills
Case math is the arithmetic that appears inside cases: percentage changes, margins, break-even, growth rates such as the compound annual growth rate (CAGR) and unit conversions, done without a calculator. The page Case math drills: percentages, growth, CAGR and break-even gives drills with answers. One drill from this guide's illustrative numbers: unit cost rises from 3.20 to 3.60, so the change is 0.40 divided by 3.20, which is 12.5%; profit falls from 0.6 million to 0.2 million, a 66.7% drop, because a small change on a thin margin is large. The trap is hidden units, such as mixing thousands and millions. Write the unit beside every number, and round inputs to friendly numbers.
Mergers-and-acquisitions due diligence
A due diligence case asks whether a company should buy another. The standard questions are strategic fit, the value of the target, the synergies and their cost, the risks and the price. A good answer separates standalone value, what the target is worth alone, from value to this buyer, which adds the synergies this buyer can capture and subtracts the cost of integration. The price a buyer should pay sits between the two, and the gap is the negotiation. The trap is counting synergies as certain. Give a range and name which assumption carries it. Candidates from finance can connect this to the investment banking guide.
The synthesis
The synthesis is the answer at the end of the case, and a strong one, as a rule of thumb, runs about thirty seconds: the recommendation, two or three reasons from the analysis, the main risk and the next step. For the illustrative case above it could run: "I recommend we first test whether the 0.40 unit-cost rise can be reversed with suppliers, because it alone cut profit from 0.6 to 0.2 million; a price rise to 5.40 would restore profit but risks volume; next I would check how customers respond to the price." The trap is summarising what you did instead of what you recommend. Start with "I recommend", then give reasons in order of importance.
Market entry case
A market entry case asks whether a company should enter a new market. The standard structure is four questions in order: how attractive the market is, how well the company can compete in it, how to enter (build, buy or partner) and what it would cost and return. It usually contains a market sizing inside it, so the habits from the market sizing guide apply. The trap is treating a large market as an attractive one. Check growth, competition and the company's right to win before the size, and end with a clear go or no-go and the condition that would change it.
Questions interviewers ask on case interviews
Questions fall into five families: structuring, estimation, math, recommendations and fit. Each is answered in one line below, in our own words.
Structuring
- How would you approach this problem? Name the goal, split it into two or three MECE (mutually exclusive, collectively exhaustive) branches, and say which you would test first.
- What would you want to know before starting? Ask about the objective, the time frame, the company's position and any constraints.
Estimation
- How big is the market for this product? Define the unit, build a driver tree, multiply rounded figures and cross-check with a second route.
- How would you check that number? Estimate the same quantity another way and compare.
Math
- Why did profit fall? Split profit into revenue and cost, with cost as fixed cost plus volume times unit cost; test volume, price, unit cost and fixed cost in turn, and find what moved.
- What price restores the old profit? Add the old profit to the new total cost and divide by volume: (4.8M + 0.6M) / 1M = 5.40. Equivalently, raise the price by the profit gap divided by volume, 0.4M / 1M = 0.40.
Recommendations
- What do you recommend? Give the answer first, two or three reasons, the main risk and the next step.
- What could change your mind? Name the assumption that would reverse the answer and how you would test it.
Fit
- Why consulting? Give a specific reason from your own experience, then link it to the work.
- Tell me about yourself. Use the present, past, future structure in the tell me about yourself guide.
For 20 full cases to practise on, use the 20 original practice cases with model solutions. For the end of the round, prepare questions from the questions to ask the interviewer page. The interview process guide shows where cases sit in the process, probability and statistics covers the estimation habits behind case math, and product management interviews use similar structures. When an offer arrives, read salary negotiation.
Follow-up questions
How do you do a case interview in consulting?
Structure the problem, ask for data, calculate and recommend, in that order, and say your thinking aloud. BCG's tips include to "clarify assumptions" and "show your thinking" (BCG careers, read October 2026), which is the habit to build first.
How do you prepare for a consulting case interview?
Learn structure and market sizing first, add case math drills, then solve full cases aloud and review each against a model solution. Prepare your fit stories in parallel, including the McKinsey PEI format if it applies, since the loop includes experience and motivation questions as well as the case.
How do you build a case interview framework?
Start from the question's goal, split it into MECE branches, and tailor each branch to the company in front of you. Use the issue tree, not a memorised list, so the structure fits the problem; the frameworks that still work in 2026 page compares the common starting structures.
How do you handle the math in a case interview?
Write the unit next to every number, round inputs to friendly numbers, and say each intermediate result. The profitability case shows why: a 12.5% unit-cost rise became a 66.7% profit fall.1
What is the difference between a case interview and a behavioral interview?
A case interview tests how you reason about a business problem you have not seen, while a behavioral interview tests what you did in your own past. Some firms add a structured behavioral segment such as the Personal Experience Interview, so prepare both.
- A case interview grades how you reason through a problem.
- Structure first, numbers second, recommendation last.
- State the unit, the assumption and the range every time.
- Open the synthesis with "I recommend".
- Prepare fit stories alongside the cases.
Sources
- Case Interview Preparation — Boston Consulting Group careers site (read 2026-10-24), 24 Oct 2026
- Interview process — Boston Consulting Group careers site (read 2026-10-24), 24 Oct 2026
- Our Hiring Process — Bain & Company careers site (read 2026-10-24), 24 Oct 2026
- Management Analysts, Occupational Outlook Handbook — U.S. Bureau of Labor Statistics (page last modified 2026-08-27), 27 Aug 2026
- McKinsey PEI: Personal Experience Interview — Yale Office of Career Strategy (read 2026-10-24), 24 Oct 2026
