Is getting good at mental math important after job offer

Question

I got through the interview process while being somewhat bad at mental math. I am a bit better at doing math with pen and paper.

Is being good at mental math valuable, important, or crucial when starting in consulting? I would assume that you do quite a lot of calculations when estimating numbers. When you do calculations: Would you usually have a pen and paper, excel/calculator, or do you often do the calculations purely mentally?

How often do you need to calculate without a calculator during your first years at MBB?

Answer 1

Hi there,

I would say it is very helpful as it allows you to quickly calculate, estimate, or sanity-check numbers in client meetings or team problem solving sessions.

You would not always have the time to pull out your laptop or phone.

I found this one of the most inspiring skills of McKinsey colleagues, being able to quickly make sense of numbers on the go, relate them to each other, and frankly, call BS if something was off. You should quickly get this intuition and pick up this skill.

Cheers,

Florian

Answer 2

It's definitely good for credibility internally and externally. You will likely be presenting analyses a lot and there will be questions from partners and clients. It's always good if you can do quick calculations on the flip chart or mentally in response to some feedback. I don't think it's the core skill you'll need to be successful but it certainly makes you look capabable

Answer 3

Hi Knut,

It's really simple: There's something you know you're not good at…and there are clear steps to get better (it's honestly just practice). So, take the steps to get better.

Will it be the end of your consulting career if you can't? Probably not. But it is important in presenting intelligence, building credibility, and, by the way, it's just an important life skill.

Dedicate an hour a day for a few weeks to doing drills and you should get there.

Answer 4

It is a good skill to have, but is not technically graded on its own. Being comfortable with mental math is useful because you will do the following very frequently

Checking your output
- You will not have the time to create checking formulas for all of your calculations
- Being comfortable with numbers helps in sense checking your output
Estimating on the fly
- This happens often, either in internal meetings or with clients
- Like others have mentioned, it is more impressive to be able to do math accurately on the fly

In addition, its also super important to be able to be comfortable around large numbers / orders of magnitude. One of the most common mistakes I've seen when I was reviewing my team's work is order of magnitude errors

Answer 5

It is a critical skill. If you can't do mental math, you are uncapable of quickly checking your own calculations. You don't need to be good at exact calculations, but must be quick (and accurate) or high level estimations.

An analyst that cannot do this is not reliable, because doesn't know when excel is giving out the wrong result (because of typos, bad programming, bad assumptions, etc.). We have excel to do the math, but we need the analyst to check the math.

For some type of projects, this is absolutely a must.

Answer 6

Hi there,

I would not worry about this but it's important to keep on practicing as mental math is helpful in multiple situations. It would not make or break your career but it's a nice to have.

Mario