The split that actually matters: budget vs rank
Google breaks lost impression share into two buckets, and they demand opposite fixes. Lost IS to budget means the campaign ran out of money before it could enter every eligible auction, so the lever is spend or pacing. Lost IS to rank means your Ad Rank was too low to clear the threshold, so the lever is bids, Quality Score, or ad relevance. Confusing the two is the most common impression share mistake. Pouring budget into a campaign that is losing to rank just funds more of the same losing auctions.
How iClick uses impression share
iClick treats the budget-versus-rank split as a triage tool before touching any bid. If a high-intent campaign is losing share to budget while hitting its return target, that is a scaling signal and spend goes up. If it is losing share to rank, the work moves to Quality Score and creative first, because buying rank with bids alone raises cost per click across the whole campaign. Brand impression share is watched as a defensive line, since a sudden drop usually means a competitor started bidding on your name.
