Cost Per Action or CPA (sometimes known as Pay Per Action or PPA) is an online advertising pricing model, where the advertiser pays for each specified action (a purchase, a form submission, and so on) linked to the advertisement.

Direct response advertisers consider CPA the optimal way to buy online advertising, as an advertiser only pays for the ad when the desired action has occurred. An action can be a product being purchased, a form being filled, etc. (The desired action to be performed is determined by the advertiser.) Google has incorporated this model into their Google AdSense offering while eBay has recently announced a similar pricing called AdContext.

The CPA can be determined by different factors, depending where the online advertising inventory is being purchased.

CPA as "Cost Per Acquisition"

CPA is sometimes referred to as "Cost Per Acquisition", which has to do with the fact that most CPA offers by advertisers are about acquiring something (mostly new customers, prospects or leads). Using the term "Cost Per Acquisition" instead of "Cost Per Action" is not incorrect. It is actually more specific. "Cost Per Acquisition" is included in "Cost Per Action", but not all "Cost Per Action" offers can be referred to as "Cost Per Acquisition".

Effective cost per action

A related term, eCPA or effective Cost Per Action, is used to measure the effectiveness of advertising inventory purchased (by the advertiser) via a CPC, CPM, or CPT basis.

eCPA is used to measure the effectiveness of advertising inventory purchased (by the advertiser) via a CPC, CPM, or CPT basis. In other words, the eCPA tells the advertiser what they would have paid if they purchased the advertising inventory on a CPA basis (instead of a CPC, CPM, or CPT basis).