8 Common Mistakes when Preparing for the McKinsey, BCG & Bain Case Interview

We have seen candidates make the same mistakes in their case interview preparation in our time as consultants and interviewers. Avoiding these mistakes can really boost your case interview preparation and help you secure a job at McKinsey, BCG & Bain.
Dec 27 / Case Interview Hub

#1 Using outdated material

Even though the case interview itself remains a core component of the case interview, other parts of the process change constantly at McKinsey, BCG, and Bain. A couple of years ago the McKinsey PST was all the rage and everyone wanted to know the secret formula to pass it. Today, it is replaced by the McKinsey Problem Solving Game (PSG) which acts as a first screening level if candidates pass the CV check. For more on the PSG and the current tests at BCG & Bain check out our article.
But this just goes to show that it is crucial that you always check what the current process looks like so that you avoid spending hours on preparing for a test that is not even in use anymore. All the major consulting firms are very transparent on how their interview process works so check out their websites. In case you pass the CV screening the recruiters will let you know anyway how the process looks like. McKinsey, BCG, and Bain also offer prep sessions where the interview process is explained. 
But don’t just look for the big themes in the process. Also check for changes to specific parts of the interview process. McKinsey, for example, added a fourth category to its Personal Experience Interview (PEI) recently - the new dimension is Courageous Change.

#2 Using unrealistic cases

Many candidates use one of the following sources to prepare for the case interview:
  • Old business school case books
  • Dedicated case books (e.g., Case in Point being the most popular one)
  • Peer cases (e.g., from platforms like PrepLounge)
The issue with these cases is that they are often not representative of what an authentic case in your interview will look like. There are several problems with these cases - they are either:
  • Too complex (e.g., because they are meant to be solved in written form) or too easy
  • Too long (e.g., because they are based on 1h interviews) or too short
  • Too industry specific (e.g., you need dedicated industry experience to solve it) or too generic (e.g., the simple profitability framework works perfectly fine)
We highly recommend that you practice for your case interview with authentic cases. You can either leverage cases from a dedicated coach (beware: there are many charlatans out there - many coaches claim that they have worked at the MBB firms when, in reality, they have never set foot in one), from friends that work at MBB firms, or you can use one of our cases. Check out our Case Simulation where you can get one case for free or check out our free case on YouTube.
Don’t get us wrong. The unrealistic cases mentioned above are not totally useless. You can leverage them for dedicated practice. For example, you can just practice structuring your issue tree or brainstorming exercises. Or you can do dedicated case math drills. If you find cases with good solutions these drills can be really beneficial to your case preparation. But just be aware that many of the cases and solutions, especially at the peer platforms, are prepared by candidates and not by experienced consultants or interviewers, so it can be the case that the solutions are off or not what the interviewer actually wants to hear.

#3 Not doing mock cases

At recruiting events, candidates often tell us that they have done 100+ cases in the last couple of weeks to prepare for their future interview. But when asking them how they did so many cases in such a short period of time, we often learn that they are solely reading through cases and solving them in written form. This definitely helps to level up your case skills as you probably have seen a wide range of cases. But we recommend to be very careful with only practicing in written form in silence. An interview is not a written university exam. You can be the best in solving cases in writing but at the interview you have to walk the interviewer through your solution. You can’t just sit down and solve the math problem, taking 10 minutes without saying a word. After taking some time to think you have to tell the interviewer what you are going to do and then you have to walk the interviewer through your calculation while you are doing it.
We highly recommend that you find a strong case partner that you can practice mock case interviews with. And if you don’t have a friend who is either strong in cases or currently a consultant or interviewer at a consulting firm, you could also consider hiring a coach for a couple of mock interviews. Just beware that you do your due diligence on the coach as there are many snake oil salesman out there. The price tag for a coach can also seem very high at first. But compared to how much money you spent on your tuition fees and the time you have invested into getting a degree and securing good internships, the price tag is actually not that high if the consulting job then acts as an accelerator for your career. Check out our article on whether candidates should spend money for interview preparation.
Another risk that comes with solving 100+ cases in silence is that you lose those cases for mock interviews. Assuming you are using authentic interview cases as per our point #2, it will be hard to find 100 - even 50 - authentic interview cases. If you want to practice cases in silence we recommend that you use the unrealistic cases for doing that and that you do the drills we mention in point #2. Leverage the authentic cases to do actual mock interviews. Our Case Interview Simulation imitates an authentic case interview and comes with a sample solution and feedback solution, with expert insights and tips. Check it out and get your first case (2h video material) for free - no strings attached.

#4 Practicing with bad interview partners

What do your parents, siblings, and preschool friends have in common? They are probably not your ideal case interview partners (unless they are interviewers at consulting firms - but then you probably would not read this article). 
Even if you don’t make one of the previous mistakes, this one can be very detrimental to your case interview preparation. We already partially touched upon this in the previous point. Only strong case interview partners will be able to simulate an authentic case interview and, more importantly, give you valid and applicable feedback. Ideally, you have a colleague or friend who is already working at an MBB firms and finds the time to do a couple of mock interviews with you. Another option is that you go to one of the peer platforms online (e.g., PrepLounge) or check out the consulting club/society at your university and look for strong case partners there. As mentioned in point #3, you could also consider hiring a coach for a couple of cases.
If you can’t find strong interview partners, having accurate sample solutions with explanations becomes even more important. Our Case Simulation gives you just that. Check it out and get your first case for free - no strings attached.

#5 Memorizing and applying standard frameworks

We are sure that you stumbled across the hundreds of case interview frameworks you can find online:
All these frameworks are helpful to understand how a case/issue tree can be structured and how to stay MECE within your structure (if you are not familiar with MECE, check out our article). But interview cases at the McKinsey, BCG & Bain can hardly ever be solved with applying a standard framework. Further, interviewers also know all the standard frameworks and they will notice right away if you are trying to squeeze a case into a standard framework even though the case requires a different structure tailored to the case.
We recommend that you familiarize yourself with the profitability framework and the business situation framework by Victor Cheng. Then you can leverage the bits and pieces from these standard frameworks and leverage them to create MECE framework for the specific case you are solving. Check out our case interview guide to learn more about how to structure an issue tree.
It happens often that interviewers, when discussing the performance of a candidate, mention that the candidate did a great job but everything seemed memorized and that it did not fit the case 100%. And if this is the opinion of more than one interviewer, the likelihood of the candidate being rejected is very high. If you want to learn more about how case performance is evaluated check out this article on how case interview performance is assessed.
So it is best to create frameworks tailored to the respective case you are solving. This can seem like a daunting task at first but after some practice it will get easier and turn into a natural process quite quickly.

#6 Overpractice

Practice makes perfect - there is no denying that. But overpractice can actually harm the outcome of your case interview. If you are approaching 100 authentic mock interview cases you will likely reach a point of diminishing return. What we mean by that is that doing more cases won’t necessarily improve your skills as you should have already mastered case interviews by then. Instead of doing more cases with only marginal improvement in your overal case skills you should consider focusing on other areas of your preparation. You should review your mistakes and work on your weaknesses.
Are you bad at case math or do you need to work on your structuring? Do some case math and structuring drills leveraging outdated case material: we mentioned in #1. Do you need to improve how you walk an interviewer through the case? Review your cases and walk and imaginary interviewer through them. Ideally also record yourself so that you can re-listen to your performance and review what you can do better.
Moreover, you should not neglect the other parts of the interview. For example, McKinsey puts a lot of emphasis on the Personal Experience Interview (PEI). If you walk into the interview with excellent case skills but thinking that you can just wing the PEI, you probably will not be happy about your interview outcome. Set time aside to prepare specifically for this part. Check out our article on the personal fit interview to learn more about it. 
All this just goes to say that once you feel comfortable with your case interview skills - so likely around 50 mock cases for the average candidate - you should think about focusing on other parts of your preparation to increase your chances of passing the interview and getting an offer.

#7 Being cheap

Let’s face it. Your starting job after university determines a large part of your future career trajectory. Of course, if you are driven you can also have a great career if you are not starting at one of the top firms but it is going to be an uphill battle.
Thus, we believe saving money on your interview preparation is probably no the best idea. Everyone in our team spent money on selective interview preparation to increase the chances of landing at McKinsey, BCG or Bain. Especially if you don’t have a strong network of friends in consulting or don’t find a good case partner, spending money on preparation can be a boost for your preparation.
Don’t get us wrong, you should not spend thousands of dollars on coaches with offer guarantees, satisfaction guarantees and so on. If you have the money to spend - go for it. But be careful that you actually find a coach who is worth the money.
In our opinion, you should spend the money on getting the right materials (i.e., authentic cases). And if you have some dollars to spare, think about doing a coaching session. There is also a lot of great free material online. Check out our Case Simulation where you can get your first case for free. If you want to learn more about whether it is worth it to spend money on interview preparation, check out our article on the topic.

#8 Neglecting other parts of the interview

Especially at recruiting events and university career fairs, you hear students ask about how to best prepare for the case interview. It seems like everything they are worried about when it comes to securing a job in consulting is the case interview. When you then ask the question whether they already got invited to the interview they usually admit that they have not even applied yet. And so they do not know yet whether they pass the first hurdle: the CV screening.
You need a stellar CV to even get invited to an interview at McKinsey, BCG, and Bain. And this is the first thing you should worry about before even thinking about the case interview. Without passing that hurdle, there is no point in already preparing for the case interview. If you want to learn more about how to craft the perfect CV check out our detailed article or our YouTube video. You can also download a free CV template in our CV excellence section.
Once you get invited to the interview you should start fully focusing on cases. But a mistake many candidates make is that they neglect the other parts of the interview. We touched upon this in #6 Overpractice. You don’t want to be the candidate that aced the case interview but failed in the personal fit interview. And on a side note: even though the process for the performance evaluation of case and personal fit interview aims to be as objective as possible, being a likeable person definitely helps.