If you are an experienced Instagram user, you definitely realize that having numerous subscribers means practically nothing. But having a lot of active subscribers is completely an opposite story. That's one of the reasons why BigBangram offers only real followers to its clients. With real people in the list of followers, there are real opportunities to win their activity.
Engagement itself is calculated based on the number of your subscribers and their activities on your account (shares, reaction to stories, comments as well as likes. Don't forget about them).
Given the fact of how people react to this or that publication, the algorithm applied by the system decides whether value of the post as well as the content itself are appropriate to let other users see it.
It's one of the incentives for people to make up various Instagram engagement groups
on different external platforms like Facebook and Telegram with a view to helping each other influence the Instagram algorithm.
In other words, the more positively your publication is welcomed, the wider its reach will be.