PostEaseNot one algorithm, but several, per surface
Feed, Stories, Reels, and Explore each run their own ranking, tuned to how people use that specific surface. What earns a Reel distribution is not identical to what earns a feed post distribution, even though the underlying signals overlap.
Watch time and re-watches matter more than a single "view"
For video, total time spent watching, including someone watching a short clip more than once, carries more weight than a plain view count. A short Reel that gets replayed can outperform a longer one watched only partway through once.
Private sends are one of the strongest available signals
Instagram's own leadership has specifically named sends relative to reach as a major ranking factor. Someone sending a post to a friend in DMs reflects real, deliberate value in a way a passive like does not, and reaching people beyond your existing followers leans on this signal heavily.
Low-effort reposting is actively worked against
An account that reposts someone else's content without adding real value risks being suppressed in favor of the original creator's own post showing up in recommendations instead. Original or value-added content has a structural advantage over plain reposting.