The measurements
- MagicPost (1.2 million posts): more than one hashtag goes with about −53%. Contested by other datasets.
- FlyPost (each author against themselves): 3 to 5 hashtags, about −7%.
- AuthoredUp: beyond 6, a negative effect. Other studies find no effect.
Reading: the direction is negative or neutral, never clearly positive. The size runs from 0 to −53% depending on source.
A simple rule
Three hashtags at most, at the end of the post, chosen for the topic and not for reach. This is a prudence rule, not a law: one relevant hashtag beats five generic ones.
Check it yourself
Keep a table of posts with and without hashtags. On your own numbers, compare with the median of your previous ten posts rather than a study average.
Paste your text in the editor, then tap “Check before copying”: flagged passages, one-click fixes, everything stays in your browser.
These figures come from observational studies published by tool vendors, not peer-reviewed. They describe correlations. LinkedIn is a trademark of LinkedIn Corporation; LinkedIn Format Pro is not affiliated with, endorsed or sponsored by LinkedIn.