Customer acquisition cost (CAC)

Average cost of acquiring a new customer. Fully loaded CAC includes all sales and marketing spend: media, salaries, tooling, and the fuzzy stuff like events and content. Marginal CAC counts only the variable cost of the next customer through a specific channel, which is the more actionable number for channel decisions.

CAC = Total S&M Spend / Customers Acquired

Match the spend window to the buying cycle: the S&M that acquired this quarter's enterprise customers was mostly spent in earlier quarters. Never optimise CAC in isolation; cheap channels that churn show up later in LTV:CAC.