Cost per action vs cost per acquisition
Same acronym, different denominators. An action is any tracked event: a form fill, an install, an add-to-cart. An acquisition is a customer. When your conversion event is not a purchase, your reported CPA prices actions, and the acquisition costs more.
Definitions
How each platform defines the A
Google: cost per action is total conversion cost divided by conversions, and you decide which actions count as conversionsGoogle Help · checked 2026. Pick purchases and CPA means acquisition; pick page-views and it does not.
Meta: cost per result divides spend by results, where the result is the campaign objectiveMeta Help · checked 2026. A lead objective reports cost per lead; a purchase objective, cost per purchase. Two campaigns, two different CPAs that share a column label.
Affiliate networks use cost per action literally: the network pays out on a defined action, sale or not. That sense lives on CPA marketing.
Materiality
When the gap changes the decision
Worked: a campaign reports a $30 CPA on trial-start actions. Trials convert to paid at 20%. The acquisition cost is $30 ÷ 0.20 = $150. If your break-even CPA is $120, the campaign that looked comfortable is losing money, and nothing in the ad account will tell you. The multiplication is the same lead-to-close math as CPA vs CPL; the danger is that both numbers wear the same three-letter name in reports.
Contracts
Which definition to write down
- In reporting: label the event, not the acronym. "Cost per trial start: $30" cannot be misread; "CPA: $30" will be.
- In agency contracts and affiliate terms: name the exact event, attribution window and dedup rule. Every ambiguity resolves in favour of whoever is paid on it.
- Internally: keep one acquisition-grade CPA (real customers, deduplicated) beside the platform CPAs. The calculator and formula page both work either definition; the input decides.