CPACost Per Acquisition (or Action)

Cost Per Acquisition (CPA), sometimes called Cost Per Action, measures spend per conversion event. The 'event' depends on the campaign goal: purchase for ecom, install for mobile, lead form submit for B2B, signup for SaaS.

CPA is platform-agnostic. Every paid-social and paid-search platform reports it, and most modern bid strategies (Target CPA on Google, Cost Cap on Meta) optimize toward a CPA goal. Acceptable CPA is determined by your unit economics: max profitable CPA ≈ contribution margin × LTV / payback period tolerance.

CPA's main weakness is attribution honesty. Platforms count conversions within their attribution windows, which usually overstates incrementality. Most mature teams cross-check platform CPA against post-purchase surveys, MMM, or holdout tests to estimate true CPA.