The advice going around is that carousels always outperform single images. Like most always-statements about social, it is a real effect described too confidently.
Why carousels do well
Two mechanics, both mundane. Someone who swipes has spent longer with the post, and time spent is a signal. And a carousel can be shown again to a person who did not engage the first time, starting on the second image — a second chance a single image does not get.
Neither of those is magic. Both depend on the swipe actually happening, which depends entirely on the first frame.
When a single image wins
- The photograph is the point — a strong image cut into six panels is a worse photograph
- You have one thing to say and stretching it to five slides shows
- You are posting often and the extra production time is what makes you stop posting
If you make a carousel, make the first slide do the work
The whole apparatus rests on slide one earning a swipe. That usually means a clear promise: the thing being explained, the number of steps, the before with the after implied. A first slide that is a title card in a nice font is a wasted slide.
Instagram allows up to ten items in a carousel, and each one is created as its own container before the post is published. That is ten uploads that can each fail, which is why a carousel scheduled by a tool should report which item failed and not simply say the post did not go.
How to tell on your own account
Compare saves and shares rather than likes. Carousels that teach something get saved; carousels made because carousels perform well get swiped past. The number tells you which one you made.