Every user of Snapchat has a Snap Score, it is a number that appears below the name of your Snapchat profile screen to track how active you are in the app. In short, it is determined by a special equation that calculates the number of snaps you've received or sent, stories you've posted, snap streak and other factors. So you have to send snaps to multiple people at once, then you'll get a bonus as well. Also, if you're maintaining the Snapchat Streaks by sending Snaps to your friends, your snap score will increase automatically.

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