Cost per action

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. Radio and TV stations also sometimes offer unsold inventory on a cost per action basis, but this form of advertising is most often referred to as "per inquiry."
The CPA can be determined by different factors, depending where the online advertising inventory is being purchased.


Differences between CPA and CPL advertising


In CPL campaigns, advertisers pay for an interested lead (hence, Cost Per Lead) — i.e. the contact information of a person interested in the advertiser's product or service. CPL campaigns are suitable for brand marketers and direct response marketers looking to engage consumers at multiple touchpoints — by building a newsletter list, community site, reward program or member acquisition program.
In CPA campaigns, the advertiser typically pays for a completed sale involving a credit card transaction.
There are other important differentiators:
CPL campaigns are advertiser-centric. The advertiser remains in control of their brand, selecting trusted and contextually relevant publishers to run their offers. On the other hand, CPA and affiliate marketing campaigns are publisher-centric. Advertisers cede control over where their brand will appear, as publishers browse offers and pick which to run on their websites. Advertisers generally do not know where their offer is running.
CPL campaigns are usually high volume and light-weight. In CPL campaigns, consumers submit only basic contact information. The transaction can be as simple as an email address. On the other hand, CPA campaigns are usually low volume and complex. Typically, consumer has to submit credit card and other detailed information.


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, CPI, or CPM basis.
In other words, the eCPA tells the advertiser what they would have paid if they had purchased the advertising inventory on a Cost Per Action basis (instead of a Cost Per Click, Cost Per Impression, or Cost Per Mille/Thousand basis).