Ad fatigue sets in when users see the same ad experience so often that they start tuning it out — or worse, start associating the app itself with the annoyance, which shows up as declining retention over time.
Vary the format, not just the creative
Rotating ad creative helps, but rotating the ad experience itself — alternating between rewarded video, banners, and capped interstitials rather than leaning on one format constantly — does more to keep the overall ad experience from feeling repetitive.
Watch retention alongside revenue metrics
Ad fatigue often shows up in retention curves before it shows up in eCPM, since users who are tired of an ad experience tend to leave quietly rather than complain. Tracking day-7 and day-30 retention alongside ad revenue metrics is the most reliable way to catch fatigue early enough to adjust frequency before it costs meaningful revenue.