CPA (Cost Per Acquisition)

CPA is sometimes used interchangeably with CPL (cost per lead), but the more precise version defines "acquisition" as whatever conversion event actually matters to the business — a completed purchase, a booked appointment, a qualified lead, depending on what's being optimized. A campaign can have a low CPA on a shallow conversion event (a form fill) and a much higher effective CPA on the event that actually generates revenue (a closed sale), which is why the definition of the conversion being measured matters as much as the number itself.

Most ad platforms offer automated "target CPA" bidding, where the algorithm adjusts bids to try to hold the average cost per conversion at a set number, spending more aggressively on auctions it predicts will convert and pulling back on ones it won't. This works best with enough historical conversion volume for the algorithm to have a real pattern to learn from — accounts with very low conversion counts often see erratic results from automated CPA bidding early on.

CPA alone doesn't say whether an account is profitable; that requires comparing it against the value of what was acquired, typically customer lifetime value. A $50 CPA is expensive for a $40 product and cheap for a $2,000 service contract.