Reach, which is the total number of people who have seen your post within the first 28 days, is counted when a post is loaded and shown in the News Feed.
Moving forward, the reach metric in Facebook Insights will include mobile data, and the desktop News Feed won’t count reach until a user scrolls and loads your post.
Previously, reach data was limited to desktop, so your Page might have been reaching more people than your originally thought. However, instead of distinguishing between mobile and desktop, it appears that Facebook will report reach as a combined total.
Additionally, Facebook noted that it will begin loading fewer stories in the News Feed. Now, when a member scrolls down the feed, more stories will load. The social network pointed out that this shouldn’t affect how many fans will see your posts in their News Feeds.
This will provide you with more accurate data regarding reach, as your stories won’t be counted until they’re loaded. Previously Facebook counted any post that appeared in the News Feed, regardless of whether or not an individual actually saw it or not.
It’s possible that you could see a drop in reach metrics due to fewer stories being loaded. However, according to Facebook, this is a much more accurate representation of your reach, which could help to adjust your outreach strategy. It’s also possible that you could see a spike now that mobile data is being counted as well.