Correct it as soon as you notice and explain the distinction briefly.

Continuing with a known conceptual error is worse than spending a little time fixing it, especially when the metric changes the business conclusion.

State what you used, what the requested metric should include, and which cost items need to be added or removed before recalculating.

Keep the correction concise and move forward once the number is fixed. Accuracy and interpretation matter more than pretending the first path was correct. case interview mental math guide.

I would rather see someone catch this themselves than confidently keep using the wrong margin.