Customer Acquisition Cost CAC (aka "cost to acquire", "acquisition cost")
The average money spent to win one new paying customer.
The fork, why two teams get different numbers
Three live definitions fight under one name. Growth/performance teams
report PAID CAC, only measurable ad spend over customers attributed to
paid channels, because it's the number they can move this week. Finance
and board decks report BLENDED CAC, all sales and marketing dollars over
ALL new customers including organic, referral, and word-of-mouth, because
that's what actually hit the P&L. A third camp (investors doing unit
economics) insists on FULLY-LOADED CAC, which adds marketing salaries,
tooling, agency retainers, and overhead on top of media. The same company
can honestly quote a $40 CAC and a $210 CAC in the same meeting.
The trap
A timing mismatch inflates or deflates it silently: the numerator is this month's spend, but many customers counted in the denominator were touched by prior months' spend (and this month's spend produces customers that close later).
- The full trap, worked on a real export
- Every formula variant, spelled out
- The reconciliation anchor, what to tie it to and when to refuse
Reference: GAAP/ASC (S&M expense classification · reference) · SaaS unit-economics convention