A guide for students · Autumn of the penultimate and final years
Case interviews explained
A case interview gives you a business problem, such as why a client’s profits have fallen, and asks you to work through it out loud with the interviewer: clarifying the question, setting out how you will tackle it, doing some maths with pen and paper and reaching a recommendation. The firms say there is no single right answer, and that what they assess is how you reason.
What a case interview is, and why firms use one
Consulting firms use cases because the interview then looks like the job. McKinsey says that for most client-facing roles you will have personal experience interviews and problem-solving interviews, and that in the problem-solving interview, sometimes called a case interview, it presents a business case to see how you approach complex problems. BCG describes a realistic business challenge, and says what matters most is how you approach the problem and the quality of your reasoning. Bain calls it a structured conversation in which you work through a real business problem, and says it is not looking for a single right answer.
None of this needs a business degree. McKinsey says it recruits problem-solvers from a wide range of disciplines, BCG that it welcomes candidates from all academic backgrounds, and LSE’s careers service that case interviews are not meant to test business or sector knowledge.
Cases you lead, and cases the interviewer leads
Cases come in two broad styles, which prep books call candidate-led and interviewer-led. In the first, you are given the problem and expected to steer: decide what to look at first, ask for the data you need and move on when you have it. In the second, the interviewer asks a series of questions in turn, such as how you would structure the problem, then a calculation, then what a chart shows, then a recommendation, and you answer each one.
The skills are the same in both. Listen to the question, repeat it back to check you have it right, ask a clarifying question or two, then say out loud how you will break the problem down before you start. McKinsey advises listening carefully and giving an answer that fits the problem rather than a standard framework, and LSE says knowledge of frameworks is not important.
Profitability, the most common kind
Many cases are about profit, because profit is revenue minus costs and so a fall in profit has only a few places to come from. Revenue is the number of units sold times the price of each; costs are fixed (rent, salaries) and variable (materials, delivery for each unit). Splitting the problem this way, and asking which of these moved, is a structure you can explain in a sentence.
Suppose a bakery chain’s profits have fallen. You might ask whether revenue or costs changed; hear that revenue is flat but costs are up; ask whether fixed or variable costs rose; learn that the cost of flour per loaf has risen by a third; and then talk through the options, raising prices, changing the recipe or the supplier, or selling more of the products that use less flour, with what each risks. The recommendation is the step people skip and the one interviewers remember.
Market sizing, with a worked example
Warwick’s careers service describes market sizing as making reasoned estimates about the size of an industry or product market, and says it often appears early in a case. Nobody expects the right number; they want a clear chain of assumptions with round figures, said out loud, and a check at the end that the answer is sensible.
How many takeaway coffees are sold in the UK on a weekday? A chain of assumptions might go: take the population as about 70 million, a round figure for the exercise; suppose half are adults of working age who might buy one, so 35 million; suppose one in five of them buys a takeaway coffee on a given weekday, so 7 million; and allow for some who buy two, so call it 8 million. Then sense-check it: if a busy café sells, say, 400 a day, 8 million coffees would need about 20,000 cafés, which sounds plausible for the whole country. Every number there is an assumption, and saying so is part of the answer.
Charts, maths and the personal interview
Most cases include a chart or table. Read the title, the axes and the units before the data, say what stands out and what it means for the question you were asked, and say what else you would want to know. For the maths, LSE suggests brushing up on percentages and simple formulae; Bain tells candidates to bring pen and paper, and writing your working down where the interviewer can follow it makes mistakes easier to catch.
Cases are not the whole interview. McKinsey’s personal experience interview asks for examples from your own life, and McKinsey suggests coming with two examples for each of the areas it asks about, leading with your reasoning and being ready for a conversation rather than a rehearsed story; BCG’s process includes interviews about your skills and about working in a team as well as a case. Some firms add an online test first, such as McKinsey’s Solve, a game-based assessment that McKinsey says needs no preparation.
How to practise
Practise with a partner, out loud, and swap roles, since playing the interviewer teaches you what a clear answer sounds like. McKinsey and Bain both publish practice cases on their careers sites, and university careers services and consulting societies often run case workshops.
With an account, cookie’s Interview prep also runs consulting case and fit interviews with an AI interviewer, which gives you the case one step at a time, asks for your structure and your maths, follows up on your recommendation and writes a report at the end. It uses credits. On the day itself, the firms’ own rules apply: McKinsey, for example, does not allow AI tools to generate answers during an interview.
Where to check
- McKinsey: interviewing
- McKinsey: the Solve assessment
- BCG: case interview preparation
- BCG: interview process
- Bain: case interview
- LSE careers: case interviews
- University of Warwick careers: market sizing
Checked against these on . The rules change from year to year, so the pages above are the ones to trust if anything here disagrees with them.
Common questions
What is a case interview?
An interview in which you work through a business problem out loud with the interviewer, from clarifying the question to a recommendation, so the firm can see how you reason.
What is market sizing?
Estimating the size of a market, such as how many coffees are sold in a day, from a chain of round, stated assumptions. The method matters far more than the number.
Do I need a business degree for a case interview?
No. McKinsey, BCG and Bain all say they recruit from every academic background, and careers services say case interviews do not test business knowledge.
Do I need to learn case frameworks?
Not as scripts. A simple split, such as revenue and costs for profit, helps you start, but firms want a structure that fits the problem in front of you, explained out loud.
Can I use a calculator in a case interview?
Plan not to. Practise percentages and multiplication with round numbers on paper, and ask the interviewer if you are unsure what is allowed.