Every ad campaign has a total number of impressions it is eligible for based on predetermined factors including budget, keywords, and bids. It is not always possible for a campaign to win 100% of those eligible impressions. When a campaign loses a portion of total eligible impressions, it results in lost search impression share.
There are a multitude of reasons for impression share loss. One main reason is the budget allotted to the campaign, which can restrict the number of times ads are displayed on the search network. Spend to Maximize Impression Share is a useful metric that can help calculate the budget that would result in minimal or no impression share loss.
Search Lost Impression Share represents lost potential. It means that your campaign could have won impressions but did not, due to factors that can be controlled and fixed. By tracking this metric regularly, you can significantly improve ad performance and get a better return on ad spend.
