The average engagement rate on the Hashtag Performance feature is based on the engagement rate of the posts with a specific hashtag. For instance, if the hashtag #dog is displayed in your Hashtag Performance and you've posted 10 media with #dog in the caption, the average engagement rate will be calculated on the engagement rate of those 10 posts.

If you have a PRO or above plan and would like to track a hashtag, then here is a how-to!