The two formulas
Engagement rate by followers divides a post's interactions by your follower count. Engagement rate by reach divides the same interactions by the number of accounts that actually saw the post. Both are multiplied by 100 to give a percentage.
Take a post with 778 interactions on an account of 18,400 followers that reached 9,200 accounts. By followers, the rate is 4.23%. By reach, it is 8.46%. Same post, and one number is double the other.
What each one is good for
By followers is the number you can calculate for anyone, including competitors, because follower counts are public. That makes it the right choice for benchmarking. It is also the number that drifts down as you grow, because large audiences include more people who rarely see you.
By reach is a judgment on the post itself. Of the people who saw this, how many cared enough to act? It ignores how widely the post was distributed, which is exactly why it is useful for comparing one idea with another.
Our rule
We report both, with different jobs.
- Use engagement rate by reach to compare posts, formats and hooks inside your own account.
- Use engagement rate by followers to compare your account with others of a similar size.
- Never compare a rate by reach with someone else's rate by followers. It will always look like you are winning.
A note on what counts as an interaction
We count likes, comments, shares and saves. Some tools add profile visits or link clicks. Neither is wrong, but pick one definition and keep it, or month-on-month comparisons stop meaning anything.
Saves and shares deserve their own line. A post where a quarter of interactions are saves and shares is doing a different job from one that only collects likes. Our calculator shows that share separately for this reason.
Report by reach to judge content and by followers to benchmark. Say which one you are using, every time.
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