Bain Round 1 - Market Sizing/Estimation and Behavioural Interviews

1st round Bain bain london
Anonymous A asked on Nov 04, 2019


I've been invited to round 1 interview at Bain London, which will be comprised of 3 interviews of 35-45 min each (1 behavioural, 1 case and 1 market sizing/estimation).

If the market sizing/estimation case is expected to take the entire 35-45 min, then how complex a question should I expect?! Most market sizing/estimation problems I expect take around 15 min max (structuring and calculation), so I'm a bit confused about how it will take up the entire length of the interview.

on Nov 05, 2019
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on Nov 05, 2019
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Hi Anonymous,

I had a similar structure for my BCG final – one case was a traditional business case, the other based on market sizing.

First of all, there will be probably some time dedicated to the fit part also in the market sizing. You will likely also have 5 minutes at the end for your questions.

Secondly, you may have market sizing as part of a case, thus also cover some business case elements as well.

Finally, you may get more than one market sizing. If you are well prepared, it is unlikely you will spend more than 10 minutes on a single market sizing – in that case, the interviewer may then ask additional market sizing questions. In my case, I got two market sizing questions and a brain teaser a part of the interview.

Hope this helps,

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market sizing can be more complex or be involved in a larger business case (I have a couple of Bain examples). Moreover, do not forget about the fit part and last questions, which will be present also in the market sizing interview and usually last 15-20 and 5 minutes.

Here some examples of 20-minute market sizing cases:


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Hi there,

usually as metioned by Francesco all the interviews with Manager/Principal/Partner (2 out 3 of Round 1) are composed by:

  • 5-10 min Fit Interview to assess if you are motivated to work for Bain.
  • 30-45 min Regular business case, with, in most of the interviews, a short market sizing. Sometimes they ask a market sizing and then a more qualitative case during the same interview.
  • 5-10 min Q&A session to verify your knowledge about Bain and motivation

Finally, the third interview is a fit interview about less then 45 min with the HR Manager. Just common questions about your achievements, weaknesses, CV, etc...


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Hi there,

you can expect the market sizing to take a good 30 minutes and I assume they can be broken down this way:

  • 40% of the time in you making assumptions and the interview challenging them. This is the core of a market sizing as the interviewer wants to tet how sound is your reasoning and how effectively you can "defend" it. Don't overthink and always perform a sanity check before stating each assumption
  • 40% of the time in doing numbers. The interviewer will want to test how good you are with calculations, and you should try to avoid any mistake. Don't rush in trying to come up with the answer as fast as possible, it's much better to take an extra 20 seconds and get it right. Also, try to make your life easy by using friendly quantitative assumptions: round numbers / percentages whenever possible
  • 20% in market sizing related questions. These can be for example brainstorming questions connected to the case (e.g. in estimating the market for pizzas in the US: "how many pizza ovens are there in the US?") or general questions connected to the final result you got in the market sizing. Try to be concise and straightforward in your answers and, again, always do a sanity check in your mind.

Hope this helped and best of luck for your interview.

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Francesco gave the best answer


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