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Arthmetic error

Had an interview  my behavioral was amazing and fantastic, I had amazing stru ture and how I drove the case was great. But I just realised I made arthmetic error. My logic was good and multiplications but my addition was wrong. This led to a wrong final figure. By a magnitude of 300k. How does this affect my outcome

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Profile picture of Federico
on Aug 21, 2026
Ex-BCG Partner, Interviewer & Career Advisor | Fully tailored approach

Hi,


Maths is just a component of what is tested in interviews, so I wouldn’t be too worried, especially considering how good all the other parts of the interview seem to have gone.

That said, it would be helpful to know the relative magnitude of your mistake as well, as 300k alone doesn’t tell much (eg was your calculation 10% off, 100% off etc…).

Best,

Federico

Profile picture of Franco
Franco
Coach
on Aug 21, 2026
Ex BCG Principal & Global Interviewer (10+ Years) | 100+ MBB Offers | 95% Success Rate

Hi,

It’s difficult to say without a bit more context: what was your seniority, and what does the 300k difference represent? Was it a small error versus the overall figure, or did it lead to a completely different order of magnitude?

What I can say is that pure calculation accuracy weighs much less than your ability to structure the quantitative problem logically and correctly.

If this was the only mistake and the rest of the interview was as strong as you describe, I would not worry too much about your chances of passing.

Profile picture of Alessa
Alessa
Coach
on Aug 21, 2026
10% off 1st session in August | Ex-McKinsey | Ex-BCG | Ex-Roland Berger

Hey there :)

Honestly, I wouldn’t worry too much. If your structure, logic, communication and case leadership were strong, one arithmetic slip is unlikely to outweigh all of that. The €300k sounds significant, but if it was clearly just an addition error and not a conceptual mistake, I’d see it as a recoverable mistake.

I definitely wouldn’t follow up about it. Just wait for the result and don’t overthink it now. If you have any further questions, feel free to reach out.

best, Alessa :)

Profile picture of Hagen
Hagen
Coach
edited on Aug 21, 2026
Globally top-ranked MBB coach | >95% success rate | 9+ years consulting, interviewing and coaching experience

Hi there,

I would be happy to share my thoughts on your question:

  • First of all, contrary to what other coaches have said, I would not automatically underestimate the arithmetic error you made for two simple reasons: 1) you don't actually know whether it was the only one and 2) you don't know how your interviewers assessed your performance.
  • Moreover, your reaction matters a lot. If you noticed the error, stayed calm, corrected the number and kept your recommendation consistent, many interviewers will not see it as a big problem. If the wrong figure went into your final recommendation without any sanity check, it weighs more.
  • Lastly, one way or another, the decision is not in your control, so I would strongly advise you to stop pondering on it and keep preparing for other potential interviews, whether with this or another consulting firm.

If you would like a more detailed discussion on your specific situation, please don't hesitate to contact me directly.

Best,

Hagen

Profile picture of Ian
Ian
Coach
23 hrs ago
Top US BCG / MBB Coach - 5,000 sessions |Tech, Platinion, Big 4 | 9/9 personal interviews passed | 95% candidate success

Hi there,

First, it sounds like you did well, but we really won't know for sure until we get the final answer.

You are not screwed. We can't say you got in, but this one incident is, in of itself, no final indication of failure.

I would actually argue that most single math mistakes are forgivable if the rest of your performance was good.

Fingers crossed for you!

Profile picture of Benjamin
8 hrs ago
Ex-BCG Principal | 8+ years consulting experience in SEA | BCG top interviewer & top performer

Hi,

Your case performance is assessed holistically. I've had candidates who had made a math mistake, but still managed to pass the case.

End of the day - the interviewer's evaluation will be a black box to you. No choice but to be patient and wait :)

All the best!