The linear decay this calculator applies above a 3.0x threshold is a planning heuristic. Real fatigue curves are not straight, and the point where they bend depends on the campaign more than on any general rule.
Three things move that point. Creative variety comes first: a campaign rotating six executions sustains far higher frequency than one running a single image, because the effective frequency of any one asset stays low. Audience size comes second, since a narrow retargeting pool accumulates frequency in days while a broad prospecting audience takes weeks. Message type comes third: a limited-time offer wears out quickly, while brand advertising tolerates and often needs repetition.
Placement matters as well. Frequency counted across feed, stories, and in-stream video treats a skipped three-second pre-roll as equivalent to a fully viewed feed post. They do not fatigue an audience at the same rate, so a blended frequency figure overstates exposure when a large share of impressions were barely seen.
Use the model to decide when to look, not to decide what is true. It is telling you that a campaign has crossed into the region where decay usually begins, which is the signal to check your own click-through trend rather than to act on the projected number.