One of the first decisions in any app marketing plan is how you'll pay for results. The two most common options — cost per install (CPI) and cost per action (CPA) — reward very different behaviour from your traffic sources, so the choice shapes everything that follows.
What CPI rewards
With CPI, you pay each time a new user installs and opens your app. Sources are incentivised to deliver installs at volume. That is useful when you need scale quickly — for a launch, a ranking push or to gather enough users to learn from.
The risk is that an install says nothing about intent. Without careful source monitoring, CPI campaigns can fill up with users who open the app once and never return.
What CPA rewards
With CPA (or CPE, cost per engagement), you pay only when a user completes a defined event: registration, first deposit, a purchase or reaching level 10 in a game. Sources must now find users who actually engage, which aligns their incentives more closely with yours.
The trade-off is volume and setup. Fewer sources accept pure CPA terms, payouts per event are higher, and you need reliable in-app event tracking passed back through your measurement partner.
A simple way to decide
- Early stage, little data: start with CPI on a controlled budget to learn which sources and geos produce engaged users.
- Clear conversion event and solid tracking: move proven sources to CPA to protect quality as you scale.
- Mature app with revenue data: manage toward ROAS targets over a defined cohort window, such as day 7 or day 30.
Many healthy programmes run a hybrid: CPI for discovery and testing, CPA for scaling what works. Whichever you choose, always judge results on post-install behaviour, not on the install count alone.