Hashtags are a tried and tested means of making a post on Instagram searchable and thus reach users outside your own followers. To counteract an ugly proliferation of hashtags, Instagram has the maximum number set to 30 hashtags per post. A lively discussion has developed in the social media community: Is it best to use only a handful of hashtags or should you exhaust the maximum of 30 hashtags?
The debate is fueled by two arguments. On the one hand, representatives of Instagram occasionally commented on the topic and recommended that no more than 10 hashtags should be used. However, they did not have the optimal interaction or distribution of the posts in mind. They expressed concern that too many hashtags in the text would not look too good. The argument can not be denied. But at the end of the day, other metrics might be more crucial for most social media managers.
A spectre is haunting us
Much more attention was therefore given to various studies that wanted to establish a link between interactions on posts and the number of hashtags used. To do this, they examined whether posts with more hashtags received more interactions than posts with fewer hashtags. Unfortunately, these studies are based on interactions per post. One study found that one should take just two hashtags, another came to the conclusion that with 1-3 hashtags you would get the most likes. A third study recommended to use exactly 9 hashtags because more hashtags would reduce the amount of engagegemt.
These results still haunt blogs and are preached at conferences. No wonder, that most posts on Instagram use a very small number of hashtags. In our study of over 5 million posts, the average was about 4 to 7 hashtags, depending on the size of the profile. Only a little more than one percent of posts used the full 30 hashtags. The more follower the profiles have the less hashtags they use.
The sad thing is that all studies described above are based on a fundamental mistake: the studies looked at the absolute number of interactions per post. According to this logic, a post is better than another if it gets more likes. For example, if a post has 200 likes, it’s better than a post that has only 100 likes.
But what if the first post comes from a profile that has 2,000 followers? And the second post is form a profile with only 100 followers? That fact changes everything. The first post, which got only 200 likes from 2,000 followers, is clearly less “successful” than the second post, which had as many likes as followers.
It’s no use building your analysis on the absolute number of likes. Especially large profiles, such as the one of Kylie Jenner with up to seven million likes per post distort the average completely. Inevitably, the studies find that fewer hashtags are optimal, because large profiles use less hashtags as seen above. In short, the studies are worthless.
In order to be able to compare the success of posts, one has to divide the likes by the number of followers of the profiles. Otherwise, a post of Kylie Jenner is always the most successful, no matter how many hashtags she uses. So if you want to discover the secret of the optimal number of hashtags, you have to compare the posts by likes per follower.
We’ve done this with 5 million Instagram posts from over 300,000 Instagram profiles. And as expected, the picture is quite different.
It is clear that the optimal number of hashtags is exactly 30 if you want to get a lot of likes on posts. The average number of likes per follower increases steadily with the number of hashtags used. The results are not only visible to the naked eye, they are also statistically detectable: There is a significant correlation between hashtags and likes per follower.
In another study, we showed that the size of a profile has an impact on the reach of posts. To make sure that the size of the profile does not distort the outcome, we have isolated the influence of the hashtags in a further analysis and statistically excluded the size. There is also a reliable correlation in this analysis: the more hashtags, the more likes. And that applies equally to small and large profiles.
Interestingly, using more than 30 hashtags is not at all advisable. Instagram does not seem to ignore the excess of hashtags but actually punishes it. Each additional hashtag seems to cost quite a bit of interaction.
The graph shows that posts with no hashtag have more interactions than posts with just one hashtag. This could be because the posts that did not have a hashtag in the text may have hidden the hashtags in comments and thus do have hashtags. But how many there are can not be determined. The result for zero hashtags should therefore be ignored.
Likes are not enough
Should you always use 30 hashtags? Definitely yes, if you aim to get as many likes as possible. Hashtags are baits for both bots and real users. However, if you do not want to optimize your posts for likes but for reach, the story is a bit different.
In a second analysis of 1.5 million posts, we looked at how much reach per follower they received, and related that to the number of hashtags. This relationship is also statistically significant and detectable. However, the findings are not quite as clear.
While the reach increases significantly with the use of hashtags, with more than 24 hashtags, it seems to be declining again. A polynomial approximation yields an optimum of 20 hashtags. Unlike with likes, it does not seem optimal to maximize reach by using 30 hashtags. However, at this point we have to point out the little presentation trick that we have allowed ourselves in the graph: The y-axis does not start at 0 but at 25% percent. As a result, the differences between the values appear much larger. The difference between 20 and 30 hashtags is only 2 percent points. This was quite different with the first analyses on likes per follower. The likes per follower of 30 hashtags were 2.5 times higher than those of posts with just one hashtag. And that is a big difference.
The benefit of hashtags is statistically verifiable, but should not be overestimated. It is an illusion to believe that with the right hashtags, the reach can be doubled. But additional interactions and reach are very likely. It is therefore advisable to use far more hashtags than currently practised. And definitely more than the often recommended 2-7 hashtags.
An easy way to find matching hashtags is to use hashtag generators, such as the Hashtag Composer.
The selection of hashtags is also very important. In no case you should always use the same hashtags or use hashtags that do not fit the post. But we will examine this in more detail in a later investigation.