CPA (Cost Per Action)

In one line

CPA (Cost Per Action) is the cost of one desired action — a signup, a purchase — calculated as spend ÷ conversions.

Why it matters

Where CPI tells you the cost of getting an install, CPA tells you the cost of getting a real, valuable action. Most campaign optimization ultimately converges on lowering CPA.

Finding the cause when CPA is high

CPA is a downstream result. The upstream metrics — CPM, CTR, CVR — usually explain why: expensive impressions, weak clicks, or poor post-click conversion.

Go deeper

Where to look first when CPA spikes is covered in Lowering CPA.