Why do I get the math part wrong everytime and how can i improve?

Hey!

First off, don’t be too hard on yourself. It’s totally normal to rely on tools like Excel or calculators when you’ve spent years in data-heavy roles—that’s what they’re there for! But I get it, case interviews are a whole different ballgame, and mental math can feel like a big hurdle when you’re under pressure.

The good news? This is absolutely something you can fix with the right practice and mindset. Here’s a game plan:

1. Build Confidence in Mental Math
    •    Start practicing basic calculations daily—addition, subtraction, percentages, ratios—until they feel second nature. Apps like Mental Math Trainer or Math Flashcards can make this easy.
    •    Use benchmarking for faster approximations (e.g., if you need to calculate 17% of 80, think of 10% + 5% + 2%). McKinsey cases rarely require exact answers, just ballpark estimates.

2. Slow Down and Check Your Logic
    •    Most math mistakes come from rushing or skipping steps. Break the problem into smaller chunks and double-check as you go.
    •    Write out your thought process clearly, even if it feels slow—it helps prevent algebraic errors.

3. Practice with Timed Cases
    •    Get used to solving math problems under time pressure. Use tools like PrepLounge or work through actual case books (e.g., Victor Cheng’s Case Interview Secrets).
    •    Have someone review your approach to spot where you’re slipping—sometimes it’s more about the method than the math itself.

4. Shift Your Mindset
    •    Remember, the interviewers aren’t just judging your math skills—they care more about how you think through problems. Stay calm, focus on the structure, and don’t be afraid to ask for a moment to gather your thoughts.
    •    Confidence is key: trust that your preparation will pay off.

Feel free to DM me to help you practice cases with a Maths component and get structured feedback! You’ve got this! 

Best,
Evelina

Hi there!

I know how frustrating this can be, as I have faced a similar issue and have worked with others that faced the same challenge. Find below what I advise you to do regarding the problems you mentioned.

1. Mental math: there are several online courses that can help you with tricks for you to perform well if the problem is a lack of technique. Probably even online YouTube videos may cover it. Watch them and do exercises and over again, I mean at least 30min per day until it is internalized. Believe me, it will.

2. Nervousness: that was my personal issue, the pressure to perform and knowing even a little mistake could cause me the offer, I would make errors that not even a kindergartner would do. There are some ways to overcome it, EFT / tapping did wonders for me. It is weird, but it works 🤷🏻‍♀️ google “math anxiety TED” 

3. Lack of method: it is key to have a step-by-step approach for you to follow. That reduces anxiety tremendously and the chances for you to make a mistake. Let me propose one for you:

A) recap what was asked, making sure you understood the prompt, what you’re expected to calculate and the numbers given. 
B) structure your equation and confirm your rationale with the interviewer. It is better to make an equation that is not complete than to make a calculation that is incorrect. Structuring will help you find out what data is missing as well.

C) perform the calculation and make your life easier by rounding when possible, using powers of tens for Hi there!

D) check if your math is right before presenting to the interviewer. It is useful to have a number to compare with. E.g. you don’t know how much is 1234 * 987, but you know that 1k*1k is 1M.

E) understand what that number means to the overall problem you’re trying to solve (the SO WHAT), what insights you take from it and what the next steps would be

F) present the result and (e) to the interviewer.

You may use the list above as a cheat sheet in your mocks/drills until you internalize it (you will!). 
 👉 Believe me, by exercising you will be able to make math a strength - you absolutely can overcome this challenge!

If you need further professional advice, math content and drills, l would be pleased to help - Just send me a message!

Best,

Mari

Hi there,

1. Math Drills
   • Use printable math sheets: Math Drills
   • Free Preplounge resource: Mental Math Practice
2. Rocketblocks
   • Great for math in the context of case interviews.
3. Key Formulas/Concepts to Know:
   • Breakeven
   • NPV (Net Present Value): With/without growth, perpetuity, and NPV 1-2 years from now.
   • % Change
   • ROI (Return on Investment)
   • Margin vs. Markup
   • Inventory Turnover
4. Structuring Math
   • Use these tips to structure math in a case:
     • Keep a separate “math” scrap sheet for calculations.
     • Start a new sheet for each phase of the case; number and title it.
     • Use tables to organize numbers.
     • Write out the equation before doing the math.
     • Always write down units.
     • Circle key numbers and write down the “so what” (your takeaway).

Hey!

Don't worry—this is a common issue, and with focused practice, you can improve significantly. Start by doing daily math drills focusing on key areas like percentages, large numbers, break-even calculations, and quick estimations. Set time limits to simulate interview pressure. Additionally, try writing down intermediate steps to minimize algebraic mistakes and double-check your work systematically. Confidence and speed will come with practice. You’ve got this! Let me know if you need more specific tips or resources.

Alessa :)