Case interview prep: a guide for beginners - Career in Consulting (2023)

This is my complete guide to case interview prep (for beginners).

When you start your case interview prep, it can beoverwhelming.

For instance, you can ask yourself: what are the interviewer’s expectations? Where to start my preparation? How to solve a case study? How do I know if I’m interview-ready?

In this case interview prep guide you’ll get:

• A (short) definition of what a case interview is
• 6xcase interview secrets: what your interviewer doesn’t want you to know
• A step-by-step guide on how to solve a case from start to finish
• Over 280 free case interview examples
• Your4-week plan to get case interview ready

All the case interview prep techniques I am going to share with you in this guide have helped over 200 candidates like you land a job in the consulting firm of their choice.

So if you start your case interview prep and target landing a job at McKinsey, The Boston Consulting Group, Bain & Company, or any other consulting firms, you’ll love today’s guide.

To begin with, case interviews are used by consulting firms in their hiring process to assess your ability to solve complex problems.

In other words, a case interview is a real client problem that you must solve in about 30 minutes during a job interview.

For instance, the problem you must solve in a case interview can be:

• Your client is manufacturing and selling cars. They have been experiencing declining sales for the past 2 years. How would you help them solve this problem?
• A grocery retailer wants to sell their products online. How would you help them take this decision?
• Can you estimate the size of the PC market in the US?

Do you want to see more case interview examples?

You can find over 280 case interview examples here.

To begin with, let me say it clearly: showing the interviewer your thinking process is MUCH more important than finding a good answer to the case.

In fact, often there are no right or wrong answers; instead, they assess your thinking process, strategic skills, and ability to justify your recommendations.

For instance, I’ve seen many candidates:

• Fail their interviews despite a good answer to the problem
• Receive an offer despite not being able to complete a case interview

In other words, your focus during case interviews should be to demonstrate strong problem-solving skills rather than to find the answer to the problem.

When the interviewer stops sharing the case prompt with you, your assessment begins.

It means that:

• You’ll ALWAYS have an ambiguous problem to solve
• The case prompt will ALWAYS have key information that is missing
• Sometimes, the case prompt will have a lot of irrelevant information

In fact, your interviewer will do this on purpose.

Why?

Because your interviewer wants to see:

• How you cope with ambiguities
• If you are able to ask the right questions to get the missing information
• Your ability to identify the irrelevant information and put this information aside

You’ll learn how to clarify a problem in the Clarify The Problem By Asking These Questions section in this case interview prep guide.

Consultants consider themselves as problem-solving professionals.

To begin with, it does NOT mean that they solve problems by luck or because they have 20 years of work experience in a specific industry.

However, it DOES mean that consultants solve problems using a logical and structured approach.

Thus, your interviewer expects the same and will test your ability to:

• Break down a complex problem into smaller, easier-to-solve problems
• Organize these sub-problems in a logical way
• Explain the relationship between an issue and the overall problem (how the issue helps solve the overall problem)

To break down a problems and organize its key components in a logical way, you need to know how to build MECE issue trees.

This case interview prep guide will define what MECE means and how to build MECE issue trees in the Develop Your MECE Issue Trees section.

Most candidates fail their case interviews.

For instance, McKinsey receives 200,000 applications per year globally. And they extend 2,000 job offers. Thus, it’s a 1% acceptance rate. Or a 99% failure rate.

So, why do so much candidates fail?

One of the reasons is because most candidates are not able to able to explain clearly the relationships between the issues (from their issue tree) and the overall problem.

Let me explain.

For instance, imagine the following case study:

“Your client is a grocery retailer operating in France. They want to enter the German market. How would you help them?”

In this “market entry” case, most (if not all) candidates would mention “competition” as a key issue.

Plus, they would ask questions such as “I’d like to know more about the competitive landscape. Can you tell me who are the main competitors and what are their market shares?”.

Which is, so far, pretty good: if you want to enter a new market, you need to understand competition better.

However, most candidates would ask only the above questions and move forward into the case discussion. And, therefore, fail to demonstrate that they understand the relationship between the issue (competition) and the overall problem (market entry).

For instance, a great candidate would say something such as:

“To decide whether our client should enter this market, we need to understand better the competition. Do we know who are the main competitors? What are their market shares? How do their offerings compare to ours? My objective is to understand how our client can create a competitive advantage and outcompete existing competitors.”

Do you see the difference?

Force yourself to always explain how an issue help solve the overall problem.

Time is money.

In consulting, this is an obsession.

Thus, consultants are obsessed to spend their time on what matters, which means on issues that have the most impact.

This is named the 80/20(or Pareto) rule: consultants prioritize their work on the 20% of issues that produce 80% of impact.

For this reason, your interviewer expects you to do the same during case interviews: prioritze the case discussion on the most important issues, and don’t get lost on low-impact details.

How to do this will be discussed in the Conduct Analyses And Find A Solution section in this case interview prep guide.

At the beginning of the case, you have around 2x minutes to build a MECE issue tree.

Thus, you have just enough time to develop an issue tree up to the 3x level.

Since many candidates learn by heart well-known frameworks (Profitability, Porter’s Five Forces, 3Cs, etc.) to build their initial issue trees, the interviewers put a potential solution to the problem after the 3x level (for instance the 6x level).

During case interviews, the interviewers ask a candidate 2x or 3x questions with an increasing level of difficulty.

Thus, they can filter out candidates that did not answer their questions and pass candidates who answered all questions.

For instance, the questions asked by the interviewers can be:

First, a “Quantitative” question such as “can you estimate the volume our client needs to produce in order to breakeven?”: it’s a question to test your ability to:

• Do logical, fast and accurate calculations
• Probe inconsistency
• Derive insights from graphs and data

Secondly, a “Business judgment” question such as “In your opinion, what are the factors that our client should consider when deciding which company they should partner with?”: it’s an open-ended question to test your ability to:

• Identify the key issues that influence the situation and develop a logical and well-structured approach
• Focus on what matters (being able to focus on the “big buckets”, not the “petty cash”)
• Come up with alternative ideas and think out-of-the-box

There are 4x categories of case studies:

• Estimate the size of something
• Fix something bad
• Take a strategic decision
• Improve something

Why this is important to categorize the case studies?

Because the category will drive how you are going to solve the case.

These are the famous market sizing questions such as:

• How many coffee cups does Starbucks sell in a year?
• What volumes of beer is sold during a LA Lakers basketball game?
• How many iPhones are currently being used in China?
• What is the monthly profit of an average hair salon in the UK?

In short, a market sizing question (or guesstimates) is a case study where you have to estimate the size of something with no (or little) data available.

These are cases where your client has a metric that is going to the wrong direction.

For instance: declining profits, declining sales, increasing costs, inefficient operations, declining productivity, etc.

It can be questions such as:

• Your client has been facing declining sales for the past 2x years. How would you help solve this problem?
• You are the brand manager of a product whose sales have been declining over the past 18x months. What would you do?

These are cases where your client has to decide whether or not they should do something.

For instance: enter a market, launch a new product, increase production capacity, acquire a competitor, etc.

It can be questions such as:

• Your client is a software reseller in the US. Should they expand internationally? To which markets?
• Should your client acquire the company [ X ]?
• Should we launch this new shampoo product?

These are cases where your client has a specific metric they want to improve.

For instance: increase revenues, decrease costs, increase profits, optimize pricing, etc.

It can be questions such as:

• Your clients wants to improve the productivity of their production facilities by 10% within 2 years. How would you help them?
• Your client wants to increase its sales by $50m in 18 months. What should they do?

First, to answer market sizing questions, you can find a complete guide here.

Secondly, to solve business cases (fix something bad, take a strategic decision, improve something – see the section above), you need to follow the 5-step process below.

Let’s see these 5x steps in details in the next 5x sections.

This first step is the easiest one: you have almost nothing to do!

In fact, your job is to listen to the interviewer and take notes. It’s not your turn to talk yet.

Based on my experience, most of candidates are doing this step right. However, here are 3x mistakes to avoid at all cost:

• Not taking notes at all. The interviewer doesn’t expect you to remember everything that he/she said
• Make your own assumptions. Do not make inferences or educated guests at this stage. I have seen candidates writing down information that was not in the problem statement
• Ask the interviewer to repeat a tremendous amount of information after he/she has finished to give you the case background

On the other hand, here is a technique that most candidates do NOT use – except the candidates I coach 😉 and that willmake you look like a Consultant and earn extra points:

Turn you page by 90° to get the long side at the bottom (like a slide), and organize your notes like this:

As discussed earlier (see the Secret #2: Case Prompts Are Always Ambiguous), you ALWAYS have to clarify the case prompt.

Yet, this is the most underestimated part of the case interview. Itsimportance cannot be stressed enough.Otherwise you might end up solving the wrong problem. And thus fail your interview.

To begin with, to clarify the problem is NOT about re-confirming the information that the interviewer has given BUT seeking out the information that he has NOT given.

To do so, I recommend using the framework below.

To begin with, if you want to help your client solve its problem or take a decision, you need to have an overview of your client’s activities:

• The product the client is selling: if the case prompt says “your client sells watches”, you should ask “what type of watches? Wrist watches? Wall clocks?” Because if you assume that your client is in the wrist watch market instead of the wall clock market, you can discuss later in the case interview a marketing strategy that is irrelevant
• Its business model: you should know how does the client make money and which parts of the value chain the client operates in (“do they manufacture the watches? Do they have their own stores or do they sell their watches to retailers?”) . This gives you a good sense of what the client can control or not
• The geography they operate in: you should know the location you’re dealing with because this directly relates to several aspects of the business such as the macro economic environment. For instance the Porshe market is probably bigger in Germany than in a developing country

Together, Product + Business Model + Geography, give you a good overview of your client’s activities and puts you in a comfortable spot to conduct effective and tailored analyses during the rest of the case interview.

This is how the client defines success.

In other words, how, at the end of the case interview, you can say that you have met the client’s objectives.

There are 2x information to clarify:

• The metric: if the case prompt says “your client manufactures cars with a sales stagnation in its electric cars division. Find out what is happening”. There is an ambiguity here: sales could mean revenue or quantity sold. If you’re not sure, a question to ask is “By sales do you mean revenue or # of units sold?”. Or in a market entry case, a good clarifying question is “what metric should we use to decide whether entering this market is a good idea?”
• The target and the timeline: ask the results that the client wants to achieve and by when. You can ask a question such as: “by how much they want to increase its sales? By when?”

The objective here is to clarify the limitations that constraint the solution scope of the problem. In other words, the constraints you should know when solving the client’s problem.

For instance, it can be:

• Internal limitations such as limited financial capacity
• External limitations such as regulation constraints

To do so, you should ask a (broad) question such as “does the client have any limitations I should be aware of?”.

This is a VERY IMPORTANT part.

Because this part helps you move from a vague problem to a list of well-defined problems (the core questions to be answered).

For instance, let’s pretend that your interviewer says “our client manufactures and sells cars. They have been experiencing declining sales for the past 2 years. How would you help them solve its problem?”.

The problem in the example above is ambiguous: what does “how would you help them solve its problem” mean?

Does that mean “understand what’s going on”? In other words, to come up with a diagnosis of WHY the client has this problem.

Or, does that mean “explore potential solutions”? In other words, to come up with a solution (an action plan) that gives the client a plan onHOW to increase its sales.

Therefore, by asking your interviewer which (core) questions you have to answer (or, in other words, what is the list of problems you have to solve), you have checked WHAT NEEDS TO BE DONE during your case interview.

Finally, here is the list of the core questions (problems) that you might need to answer (solve) by case category (see the section Know Your Enemy: The 4x Categories Of Case Studies).

Thus, your job at this stage is to check with your interviewer which core questions you have to answer.

For instance, with the example above, do not assumer that you have necessarily to find out why the client has been experiencing declining sales. Maybe they already know. Thus, your job is to determine a solution.

Building MECE issue trees is the most challenging part for most candidates.

In these free courses, you’ll get the 3x techniques to develop MECE issue trees.

In the following courses, you’ll get how to communicate your conclusion to your interviewer.

It’s very important to have a structured and fact-based conclusion. Let me show you how to do so.

You have a case interview planned at Mckinsey, the Boston Consulting Group or any other consulting firms soon? You don’t know where to start your case interview prep?

Here is a 4-week plan to get ready for your case interviews.

Let me give you three other tips to succeed in your case interview prep:

First, you can find over 280 free online case interview examples here if you run out of cases.

Second, if you want personalized feedback from an expert, it’s here.

That’s it for this case interview prep guide.

And now I’d like to hear from you:

Do you have any questions about case interviews? Or about the 5-step process?

Or maybe there is something I didn’t include here.

Either way, let me knowby leaving a comment below right now.

Sébastien Ritter