Tweets with hashtags get two times more engagement than tweets without.
This data, courtesy of Buddy Media, is one of the most-cited examples of the effectiveness of hashtags, and for good reason: doubling your online engagement is a big deal! Imagine going from four retweets to eight or 10 retweets to 20. And all it takes is a simple # or two?
Apparently so. Although, you’ll want to keep it to no more than two.
Buddy Media’s research also showed that the volume of hashtags bears monitoring: one or two hashtags appear to be the max. When you use more than two hashtags, your engagement actually drops by an average of 17 percent.
Twitter’s own research into hashtags confirms that there is significant advantage to using them. Individuals can see a 100 percent increase in engagement by using hashtags (the same bump as seen in the Buddy Media study). Brands can see a 50 percent increase.
Engagement, as measured in these studies, can include clicks, retweets, favorites, and replies, yet if it’s only retweets your after, hashtags still would be a smart bet.
Tweets with one or more hashtag are 55 percent more likely to be retweeted.
With thanks to buffer: https://blog.bufferapp.com/a-scientific-guide-to-hashtags-which-ones-work-when-and-how-many