Maths and details in Case interview

Hi there — a lot of candidates struggle with this, so you're definitely not alone. Math and information management are very common pain points in case interviews.

1. What math concepts should you focus on?

Case interview math is usually not complicated, but it requires being structured, calm, and communicative. The most useful concepts to master are:

Core calculations (non-exhaustive)

• Percentages (e.g., 20% of 250, % growth/decline)
• Ratios and proportions
• Multiplication and division with round numbers
• Weighted averages
• Breakeven calculations
• Market sizing arithmetic
• Growth rates (rough YoY changes)

Techniques to make math easier

• Round numbers strategically (e.g., 49 → 50)
• Break calculations into steps
  Example: 24 × 35 → (24 × 30) + (24 × 5)
• Say your approach before calculating
  “I'll first multiply revenue per unit by volume to get total revenue.”

Communicating while calculating
You don't need to do everything simultaneously. A simple structure works well:

1. State the formula
2. Plug in the numbers
3. Calculate step by step
4. Give the final answer with interpretation

Example: “Profit equals revenue minus costs. Revenue is $50 per unit × 200 units, so that's $10,000. Costs are $6,000. That leaves us with a profit of $4,000.”

Interviewers care more about clear thinking than speed.

2. How to manage information and avoid forgetting things

This is usually a note-taking structure problem, not a memory problem.

A simple approach:

Divide your page into sections

Left side:

• Case objective
• Key question

Middle:

• Structure/framework

Right side:

• Numbers and data

Bottom:

• Insights/conclusions

Also:

• Circle key numbers
• Write units clearly ($M, %, units)
• When new data appears, quickly summarize it out loud
  (“So we have 3M customers and $20 average spend.”)

This reduces the need to memorize because everything is visible on paper.

3. Should you practice with peers?

Yes, this is actually important to do.

Practicing alone helps with understanding the flow, but case interviews are interactive. You need practice with:

• Explaining your math verbally
• Thinking under pressure
• Structuring out loud
• Handling interviewer questions

Messing up during peer practice is exactly how you improve. In fact, candidates who only practice alone often struggle more in real interviews.

Even if the math goes wrong, you’ll still learn:

• How to communicate your logic
• How to recover from mistakes
• How to slow down and structure calculations

One extra tip for math mistakes

Many candidates rush because they think speed is expected. In reality:

Accuracy + clear communication > speed.

It’s perfectly fine to say: “Let me take a few seconds to calculate this.”

That small pause often prevents most mistakes.

If you need help working through these challenges, feel free to reach out — happy to help with more specific coaching.

Five months of solo prep is actually part of the problem here. Let me explain.

On case math

You do not need complex concepts. The math in cases is mostly percentages, ratios, market sizing, and basic arithmetic. What trips people up is not the concepts, it is the pressure.

The fix is deliberate daily practice. Ten minutes every day, mental math drills, percentages, large number multiplication, working without a calculator. Do this for 4 weeks consistently and the speed comes.

For communicating while calculating, narrate your steps out loud as you write. "I am going to multiply revenue by margin to get profit, that gives me roughly..." It slows you down slightly but stops you from going silent and losing the interviewer.

On forgetting details

This is a note-taking structure problem, not a memory problem. Build a simple template on your paper at the start of every case. Box for the problem, box for data given, box for your structure. Write every number down the moment you hear it. Do not rely on memory at all.

On peer practice

Do it. This is exactly where you need it. Messing up in practice is the point. You will not learn this by practicing alone because the pressure of being watched is what you need to get comfortable with.

Solo prep builds familiarity. Peer practice builds resilience. You need both.

Hope this helps, good luck with the process.

Hi,

1. Math in case interviews
You don’t need advanced math; focus on basics such as percentages, growth rates, ratios, breakeven logic, and quick multiplication/division. Structure the calculation first, then do the math step by step out loud, and close with a short takeaway (e.g., what the result means for the case).

2. Managing information
Be disciplined with note-taking. Write numbers clearly, group information by topic (revenues, costs, market, etc.), and circle or box key figures so you can easily refer back to them later in the case.

3. Practicing effectively
Peer practice is still very useful. One thing that can help is doing one session with an experienced coach to get targeted, professional feedback on your math and communication. After that, you can go back to peer practice with clear points to focus on and improve much faster.

Hi! What you're facing can be a common challenge for others too. Based on the context you've shared and your questions, here's what you can do:

• Improve note-taking: Synthesis is a very important skill during case interviews. It means being able to note, reflect on, and link information at every step of the case with each other as well as with the overall business problem you are solving for. It is vital throughout the case, as well as during maths
• Structure case maths: Maths in cases has to be treated like a mini case - you should structure (i.e. set up an equation) to understand what variables you will work with to solve the problem and then use information from the interviewer, together with any agreed upon assumptions, to fill in gaps in that equation
• Practice live: There is no replacement for live practice. You must put yourself in this situation multiple times a week to be comfortable with delivering under pressure and tight timelines. Feedback from case, if reviewed and implemented well, can lead to significant improvements in your performance. Even if you feel uncomfortable, at the very least it will enable you to understand how to continue to be confident and professional if faced with such a situation in a real case too

Happy to work with you in depth on this particular skill as well as broader case prep. Feel free to reach out and good luck! 

I strongly recommend you get some professional support on this. 

It sounds like you've put in a lot of work, but at this point, you've plateaued and are making the same type of mistake over and over. 

Most likely, your issue has to do with the technique with which you're approaching calculations. As long as the technique is not right, more practice is not the answer.

If you need any help, reach out. Calculations are one of the areas I emphasise with my candidates.

Also, you might find the following useful:

• • Cheatsheet: The Must-Know Consulting Terms for Interviews

Best,

Cristian

Hey there :)

For case interview math you mainly need comfort with percentages, growth rates, breakeven logic, margins, and quick multiplication or division with rounded numbers. What helps most is slowing down slightly and speaking your logic step by step rather than trying to calculate and explain everything at once. Many candidates improve a lot by writing the calculation clearly, doing the math first, and then explaining the result and the implication.

For remembering information, a simple structure on your page helps a lot. Many people keep one area for key numbers and assumptions and another for calculations. That way you always know where to look instead of trying to remember everything mentally.

And yes, practicing with peers is actually very helpful for this problem. Even if you make mistakes, that’s exactly how you learn to communicate calculations under pressure. Most candidates only become comfortable with the math once they start saying it out loud in real case practice.

If you want, feel free to reach out with more questions anytime.

Best,
Alessa :)

It's incredibly common to feel stuck on the math and information management – those are often the hardest parts to master and where candidates tend to differentiate themselves. The truth is, the interviewer isn't always looking for you to be a human calculator, but rather to see your structured thinking and process.

For math, the trick is to verbalize your steps as you go. Don't try to do it all in your head and then deliver the final number. Instead, say "Okay, to get to X, I'll first calculate Y by multiplying A by B. Then I'll divide that by C." This lets the interviewer follow your logic, correct you if you're going down the wrong path, and understand how you're approaching the problem, which is often more important than getting the exact answer instantly. Practice the basics – percentages, ratios, powers of 10 – until they're second nature, always talking through them out loud. For remembering details, a robust note-taking system is non-negotiable. Structure your notes clearly (e.g., using headings for different case areas, bullet points for key facts, dedicated space for questions) and periodically recap the core information to yourself and the interviewer to ensure you haven't missed anything crucial.

Regarding peer practice, absolutely do it. The fear of messing up is precisely why you need to practice with others. That pressure, those mistakes, and the immediate feedback are invaluable. It's the only way to truly simulate the interview environment and build the muscle memory for talking through math or managing information under stress. You'll quickly learn where your notes break down or where your verbal math logic isn't clear.

Hope this helps! All the best.