Frequency capping — limiting how many times a given ad format can appear per session or per time window — is the single most effective lever for keeping ad monetization sustainable without tanking retention.
Cap by trigger, not just by timer
A fixed timer (one interstitial every 90 seconds, say) is easy to implement but ignores what the user is actually doing. Capping by trigger — one interstitial every third level, one every content transition — tends to feel far less intrusive, because the ad shows up at a natural pause rather than an arbitrary moment.
Revisit caps as the app changes
The right frequency cap isn't a one-time setting. As session length, content volume, or audience composition shifts, the cap that worked at launch may start suppressing retention or leaving revenue on the table — which is exactly what periodic A/B testing of the format mix is meant to catch.