Not automatically. One arithmetic mistake does not by itself determine the entire interview.

What matters is the size of the error, whether your setup was logically correct, how much help you needed and what you did after the interviewer corrected the number.

If they give you a number and move on, accept it, recover quickly and continue the business reasoning. Do not spend the next five minutes apologizing or mentally replaying the mistake.

Repeated errors or an inability to explain the calculation are more concerning than one slip. Build a simple checking habit before stating the result. The case interview mental math guide covers ways to make calculations more reliable under pressure.

I had one correction in R1 and still advanced. The rest of the case matters.

My worst mistake was letting one math error destroy my confidence for the next ten minutes.