Customer Acquisition Cost (CAC)

CAC is total sales and marketing spend divided by new customers acquired in the same window. The arithmetic is trivial; the definition isn’t. Whether sales comp is counted when earned or when paid, whether the window is three months or twelve, and which marketing costs are attributable at all can move the result by a wide margin before anyone has done anything wrong.

CAC only means something once that window and cost boundary are pinned down and held constant. See CAC payback period for how the same ambiguity compounds once CAC feeds a second metric.