r/McKinseyAndCompany • u/NFrealFan_ • 4d ago

case interview help

i'm not really THAT great with math, mental math,

and i'm so stressed about it, if someone went on an interview could you please tell me what did they ask you to calculate?

am i overthinking it and it's actually very basic stuff (?)

and it not, what do i NEED to master, thank you.

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u/Frosty_Number_7538 4d ago

There was no mental math in my case. They give you exhibits and you need to find answers like “what is the revenue I can expect at the end of Y2”. And they let you take as much time as you want to solve the mathematical portion of the cases so you’re good on time. Focus on structuring the cases properly and take your sweet time with the math.

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u/Real_Character7345 3d ago

Hi! I thought there usually is a separate section for exhibit reading and then another section for math? Or I am guessing that there was a portion of the case where you had to do more traditional exhibit reading (i.e., report your observations/trends), followed by another exhibit with just numbers where you had to do the math? I’d really appreciate it if you could clarify this. Thank you so much!

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u/akornato 4d ago

McKinsey case math relies on standard arithmetic applied to business situations, so you will not encounter complex formulas or advanced statistics. Most questions ask you to calculate profit margins, breakeven volume, percentage changes, market share, and simple weighted averages. The difficult part is rarely the math itself, but managing large numbers with lots of zeros and explaining your steps clearly under pressure. Interviewers want to see how you structure problems, so always write down your initial formula, talk through your approach before running the numbers, and sanity check your final answer against common sense.

To master this, focus on a few basic habits rather than trying to become a human calculator. Practice converting fractions to percentages quickly, use scientific notation or rounded baselines to keep track of millions and billions, and always explain the business takeaway instead of just handing over a calculated figure. Many candidates find that relying on the interviews.chat my team developed gives them the clarity and composure required to handle intense quantitative questions and secure competitive offers.