The ultimate guide to consulting case interviews

You cannot wing your way into a job at a top strategy consulting firm.

What is the case interview?

Consultants essentially solve business problems for clients. In a case interview, you will be asked to solve a business problem for a hypothetical client in 25–45 minutes. These cases tend to be based on interviewers' real case experiences. There is generally no right or wrong final answer; the interview is testing your core casing skills. These skills are structured thinking, good communication, fast and accurate mental maths, business acumen and creativity.

Example case

A fast-food chain based in the US has been unprofitable in the last 2 years. The CEO has asked your consulting company to figure out why this is the case and come up with ideas to increase profits.

1. You will begin by asking some clarifying questions, e.g. by how much would the CEO like to increase profits and by when.
2. You will then create a framework that helps you tackle this problem. This framework should indicate structured thinking and creativity. For example, here, you may break this problem down into two main buckets: revenues and costs. Within the revenues bucket, you may choose to split revenues by products, and compare the revenues of your client to its competitors. On the costs side, you may split this down into fixed and variable costs, and specify each of the costs that a fast-food chain specifically may face.
3. You would then suggest some sort of hypothesis for where you want to start, e.g. "I think that a decrease in revenue may be the driver of this fall in profitability. Do we have any information on our client's revenues over the last 3 years alongside its competitors' revenues?" A consultant cannot research and analyse every potential relevant factor. They charge by the hour and that would be very expensive. You must learn to prioritise and use the 80-20 principle.
4. The interviewer is likely to give you some data at this point or point you towards a different part of your framework if they think that another area is worth beginning with. With data, your interviewer is testing two things: your ability to perform mental maths, and your business acumen, tested through your ability to draw key insights. After this, you may have reached a sufficient hypothesis for why the business is unprofitable, or you may require more information. If so, ask for it.
5. You may then brainstorm ways in which the firm could boost profits over the next 3 years, addressing the second part of the prompt. Here you should try and structure your brainstorming, think creatively, and communicate your ideas well.
6. Finally, you are likely to have to present a recommendation for the client. Here you should summarise your findings and communicate in a top-down manner.

General advice

Once your CV is great and you've smashed whatever tests the company has thrown at you, your achievements and background no longer matter (outside of fit interviews); all that is important is how well you case.

Here are some very important pointers I picked up on:

1. Do not learn the kind of frameworks you might find in books or on the internet. Practise building your own frameworks.
2. Read a casing book, e.g. Victor Cheng or Marc Cosentino, but only skim through them so that you get a sense of the key takeaways but don't become robotic.
3. Make a PrepLounge account. Get the premium version. Do lots of live cases with strangers.
4. I would recommend practising 15–20 live cases over 3 months, i.e. 1–2 cases a week. Ensure that between cases you are actively trying to take on board feedback from your previous case by doing drills. For example, if you received feedback that your framework was not very comprehensive, find a casebook, read a prompt, and just draw out a framework for that case by yourself. Repeat this until your frameworks seem to be getting better. You don't need to go through the entire case; just drill the parts that you are weaker at.
5. When you find a good casing partner, keep hold of them. Find someone who you can learn from, and that gives you good, comprehensive feedback. Set up regular casing sessions with them.
6. After every few cases, try to find ways to improve your overall approach to casing. Go back and read new websites, or look at the tips in case books. Often someone will suggest a way in which you could tackle recommendations or mathematical questions that is better than how you are currently doing it.
7. Practise your mental maths. Even if you have a degree in maths, this is worth doing. Practise long multiplication with lots of 0s under time pressure, and learn basic consulting formulas, e.g. breakeven, payback period, profit etc. There are lots of sites where you can do this, e.g. Zetamac, Management Consulted and CaseCoach.
8. Get a CaseCoach subscription. It is worth it for the drills and particularly if you have any written or presentation cases. My Strategy& structured case studies were in the same format as the practice cases on the CaseCoach site. You can also use Crafting Cases for drilling.
9. Try to case with a current or ex-consultant at least once. Bain partnered me up with a current associate consultant once I received an interview invite, and we did 2 practice cases over weekends. The feedback that you get from 1 practice case with a current or ex-consultant is equivalent to 5 practice cases on PrepLounge.
10. Watch videos of people casing. If you are a member of SEO, go to your portal and watch the Step into Consulting videos. These are all led by great casers at MBBs, and the advice is invaluable.
11. Don't overdo it and burn out. I tried not to case or think about casing for at least 1–2 days before an interview. Do lots of activities to take your mind off things: go to the gym, meditate, do yoga, go for dinners, and go to the cinema. Get a good night's sleep for 2 days before your interview.

Specific advice for casing

This guide is predominantly for amateur or novice casers. If you are a complete beginner, I'd recommend reading a book or watching some videos first (use YouTube) to see how casing works and get familiar with the format.

Communication

If you're a good communicator and speak in a structured manner, I have found that this is enough to pass you through almost all case interviews.

• Be top-down. Use the Pyramid Principle.
• Over-communicate. Really lay out everything you've written down, particularly for frameworks, and ensure your interviewer can envision it. Walk them through your approach for maths as well, even if it seems simple to you. If they can't follow you, they can't help you.
• Use short sentences.
• State your assumptions.

Introduction

• When you first get the case, say "Thank you, this sounds really interesting, let me summarise the case."

• Repeat it back to them and check if you've missed anything.

• Come up with clarifying questions, usually concerning three things:

  1. Clarifying any terms or ideas that you don't understand from the prompt.
  2. Quantifiable goals, e.g. is the aim of the company to increase revenue or profits? What % do they want to increase profits by and by when?
  3. The business model or industry structure: understand sales and distribution channels, key geographies that the firm operates in etc.

  It's really important not to get too detailed here with questioning. Keep it very high level, just enough to build a framework.

• If it's difficult to understand the situation, suggest a real-life proxy, e.g. if it's a case about a fast-food chain selling burgers, think about McDonald's. This will help you to frame your ideas.

Framework

• When you fully understand the case, take a moment to structure your thoughts.
• Think high level and have very broad buckets at the top level, spanning from market to implementation. Think like an entrepreneur: what areas would you need to consider to tackle this problem?
• Within each bucket, think of specific factors that would be important to look at.
• Ensure that the wording of these factors is very specific and tailored to the case so that it doesn't seem like you are regurgitating a framework that you've learnt. This also enables you to get creative.
• Identify where to start based on a current hypothesis or what is likely to be the most important factor. Ask the interviewer if they have any data in this area. This is you leading the case.

Maths questions

• When you get numbers, structure your mathematical approach and outline it to the interviewer. Get their confirmation before plugging in numbers.
• Consider any exceptions and discount them.
• Then go and do the maths.
• Make net impact calculations etc. Don't just talk qualitatively with no numbers to benchmark things.
• React to numbers: say if you think that they're big or small. Suggest if you think there are any major missing variables or any major assumptions that are driving these numbers.
• Always suggest the "so what" after reaching a number. What does this mean for the firm in terms of the original business problem? Do we need to adjust our hypothesis based on this finding?

Graphs

• When you get a graph, say what this graph is telling you in one sentence and point out 1–3 key insights.
• Ask about any inflexion points or anomalies.
• Suggest the "so what" of these key insights.
• Adjust your hypothesis based on the graph and then think about what should be explored next.

Brainstorming and creativity questions

• Structure your brainstorming by laying out buckets within which your ideas fall.
• Try and come up with unique and creative suggestions.
• It's important here to show a broad range of ideas. Really think outside the box and suggest as many things as you can. If the interviewer feels like you're taking too long they will move you along. It's not your job to do time management here (at least for interviewer-led cases).

Conclusion

• Begin by answering the prompt.
• Use the data that you've been given through the case, and ensure that the insights that you've drawn back up your recommendation.
• Outline 1–2 key risks that the client might face with this recommendation. This could be based on some of the assumptions that you've made.
• Outline next steps: what else should the client look into, and an implementation plan.

Other advice

• Don't be afraid to ask for time once you're presented with some information. This will help you to come up with better ideas and structure your thoughts.
• Expect the unexpected, particularly for final round interviews, and particularly for MBB.
• You may find that the interviewer guides you through the case in a way that suits them. They may miss out significant parts of the case, e.g. they might not give you time to ask clarifying questions after the prompt, or they may jump straight into data without you creating a framework first. Go with the flow, and this is why ensuring that you have the 5 core skills will get you through any case: structured thinking, good communication, fast and accurate mental maths, business acumen and creativity. If you fail a case interview, it is very likely to be down to a weakness in one of these 5 areas.

You only get to the case once your CV has passed the screen. The CV review scores yours against what consultancies look for.

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