My interviews in three weeks - what should I do?

Question

I have interviews in the next three weeks for an internship with MBB (McKinsey, BCG, Bain), focused on case interviews. From my practice over the past two weeks, I've gotten used to taking cases, but I’ve noticed that I struggle with calculations, drawing conclusions, and understanding what a particular number means.

I often can't deliver a solid recommendation when I get lost in the calculations. I often set up the formulas correctly, but I find it particularly difficult when dealing with four or more numbers. Additionally, I’ve noticed that I take a long time to do the calculations, even when using shortcuts like k×k=m and so on.

Will this negatively affect me during the interview? I mean (long time to make calculations)
How should I improve calculations, drawing recommendations, and my judgment skills?
How many cases should I be taking in the upcoming weeks on a weekly/daily basis?

Answer 1

Hi there,

First of all, congratulations on the invitations!

I would be happy to share my thoughts on your questions:

First of all, given the still quite extensive weaknesses, I would highly advise you to consider working with an experienced coach like me in order to accelerate the process and enhance the quality of your preparation.
Moreover, I would advise you to practice written math daily using tools like PrepLounge’s Mental Math Tool to improve calculation speed and accuracy.
Lastly, considering your interview is in just three weeks, I would advise you to prepare on a daily basis, even if this doesn’t necessarily mean that you have to solve a case study.

You can find more on this topic here: How to succeed in the final interview round.

If you would like a more detailed discussion on how to best prepare for your upcoming interviews, please don't hesitate to contact me directly.

Best,

Hagen

Answer 2

Hi there,

It’s great that you are preparing in advance for your MBB case interviews! Let's address your concerns systematically and outline an effective preparation plan:

1. Will slow calculations negatively affect you?

Yes, slow calculations or getting lost in them can be problematic in case interviews. However, interviewers aren't only evaluating the accuracy of your calculations, they want to see your logical approach, mental agility, and ability to derive insights from the numbers. That said, with three weeks, you have enough time to improve and become more comfortable with calculations and conclusions.

2. How to improve your calculations, judgment skills, and recommendations?

Calculations:

Practice Mental Math: Dedicate 15-20 minutes daily to mental math exercises, focusing on multiplication, division, percentages, and ratios. Mental Math Trainer or Victor Cheng Math drills are great to do this.
Use Estimation: In case interviews, approximation is often acceptable to save time, but always check with the interviewer first. For instance, you can round numbers (e.g., using 370 or 375 instead of 374 or 374,4) to simplify calculations. Typically, interviewers are fine with rounding once you've demonstrated precision on a key calculation. After confirming, continue using estimates for faster progress while keeping the overall structure and logic intact.
Break Down Calculations: When you see multiple numbers, break them into digestible parts and calculate in steps, writing out important pieces of information. Use common shortcuts like multiplying by 10%, doubling, halving, etc.

Judgement skills / Recommendations:

Link Numbers to the Big Picture: For every number or calculation result, explicitly think about what it means for the business situation and whether it supports or disproves your hypothesis and mention that as a short conclusion to the interviewer.
Practice Summarizing Findings: After each case, summarize your results out loud or in writing. Focus on key insights, why they matter, and what actions you'd recommend based on them.

3. How many cases should you take in the next three weeks?

The number of cases you should aim to do depends on your current level, but since you’ve already started practicing, here’s a structured approach:

Daily Practice: Aim for 1-2 cases per day, focusing on different types (profitability, market entry, growth strategy, etc.).
- Start with 1 solo case per day: Do cases by yourself to get familiar with frameworks and then take time to pause and reflect on your thought process and calculations.
- The second case can be with another applicant or coach: This will allow you to simulate real-time interview pressure and get feedback on your structure, speed, and delivery.
Weekly Goals:
- Week 1: Get familiar with the general case types and focus on improving calculation speed and accuracy. Do 7-10 cases this week.
- Week 2: Sharpen your ability to draw insights and conclusions quickly. Aim for 10-12 cases this week. Mix up different types of cases to expose yourself to various scenarios.
- Week 3: Finetune your communication skills and recommendations and work on how you can shine compared to other applicants. Aim for 7-9 full-length cases. And don't forget to prep your personal interview, which is also as important!

In total, aim for around 25-30 cases (depending on your skill level) over the next three weeks, along with dedicated time to mental math practice and structured feedback sessions.

You have enough time, just practice consistently!

If you need more help to come up with a detailed plan and/or coaching sessions to work on your weak spots, let me know. We can also focus on drills to improve your calculation and judgement/recommendation skills.

All the best,

Kairavee

Answer 3

Hello there,

Unfortunately, taking too much time during calculations could hamper your chances during the interviews.

From the context given, it appears you understand the basics of how case interviews work so I’d suggest you focus on the following steps to improve calculations, business judgement, and derivation of the so-what:

Detailed baseline assessment: Conduct mock interview with a case coach / consultant / experienced interviewer to identify additional weaknesses beyond your initial findings and suggest pragmatic methods to address them within the next 3 weeks
Identification of specific drills: Seek specific drills that are targeted towards addressing those weaknesses (e.g. structuring drills for tailored frameworks, maths drills for quicker case maths, etc.)
Drills & case practice: Alternate practice between drills and complete mock interviews iteratively so you can adjust based on feedback. Quality of interviews and drills here is a lot more important than the number completed so there’s no magic minimum number
Fine-tuning and fit preparations: In the final days before your interview, conduct mock fit sessions to ensure communication is crisp and that you exude the desired executive presence

Feel free to reach out if you need support with any of the suggested steps above.

All the best,

Fathu

Answer 4

Hey there,

A few thoughts:

The key reason why candidates fail their case interviews and don't improve with practice is because they never learn the right approach and techniques to begin with. They might go through 30-40 cases, just repeating the same mistakes over and over again. There is often no strong baseline.
So even if your timeline is compressed, make sure you understand and learn the basics for each part of the case (structuring, charts, math), which is
- A replicable step-by-step for each part of the case interview
- The right thinking techniques around the individual parts (e.g., what's a framework, what is evaluated, how can I ensure I think about it the correct way, what are some shortcuts to get to the answer quickly, etc.)
- Simple communication templates to help you communicate your insights as well as ask for data in the right way to drive the case forward
There are several approaches you can take, such as hiring a skilled coach, reading the right materials, or enrolling in relevant courses. For example, while some chatbots may suggest a list of books, my book, The 1%: Conquer Your Consulting Case Interview, provides direct guidance tailored to modern case interviews. It covers all the essential points mentioned here, and more, while also offering a detailed preparation plan. You can find it on Amazon
Avoid generic advice and framework memorization approaches. This will only hurt your performance and waste a ton of time (why -> check out the first post here: https://www.preplounge.com/en/consulting-forum/how-goodrelevant-is-the-case-in-point-book-for-case-prep-1984)
Once you have that baseline it's time to practice and internalize the skills to create the right profile, polishing your strengths and lifting your weaknesses to a robust-enough level
Practice drills alone (structure, chart, math) and practice full cases with other excellent candidates that know the right habits and approach. It is crucial that you are practicing with really good peers, otherwise, it's a waste of time. Practicing drills on your own is a huge effectivity and efficiency booster since you can go over many more questions in a shorter amount of time compared to practicing with peers. Do both in parallel! You want to spend your time where it is most useful, e.g., if you struggle with math focus on math drills, etc.
Focus on quality over quantity. Doing 50+ cases does not mean much if you are not applying the right habits to score high and do a detailed debrief after every case to improve. You want to move from bad to good for your weaknesses and good to great for your strengths --> use the feedback from your previous experience and tailor your prep accordingly
Consider booking at least an initial coaching session to get a detailed and objective evaluation of your performance + learn the right habits for every case regardless of context and framework + get a tailored preparation plan out of the session that will set you up for an effective and efficient prep.
For your prep, tailor the cases to the firm you are applying to. McKinsey cases for instance are quite different from BCG and Bain
Don't forget the fit interview part. Prepare answers for all the typical fit questions and stories (3-5 hours) and rehearse them a couple of times (5 hours)

All the best with your prep!

Cheers,

Florian