To fully understand your Organic Traffic Insights data, its important to know the difference between two key metrics, Sessions, and New Sessions.
A Session is defined by Google as a user’s interaction on a website that takes place within a set time frame. By default, Google sets this time frame to 30 minutes.
If this is a user's first time interacting with a site they would be considered a New Session. A single user can have multiple sessions but can only be counted as a new session once. So how can a user have multiple sessions?
Let's use Google's default time frame as an example. If someone visits your site, leaves, and returns within 30 minutes it would count as one session.
However, if a user visits your site, leaves, and returns after 30 minutes of inactivity, their return to the site would be counted as another session. This is why a new user can create multiple sessions.
Keep in mind you are able to change this time frame within Google Analytics to fit the goals of your campaign.
As defined by Google Analytics, “% New Sessions” is the percentage of all first-time visits (sessions) out of the website’s total visits.
Let’s say there are two Internet users: John and Ashley. John has never been to Amazon.com before while Ashley visited the website 4 days ago.
Today, Ashley visits Amazon.com (as a returning user) and shops around for a pair of shoes. She takes a lunch break and leaves her computer for longer than 30 minutes. When she gets back from lunch she returns to Amazon and continues shopping. This will count as 2 sessions on Amazon.com but neither of them are new sessions.
If John were to have this same exact interaction with Amazon (visiting the site for the first time, leaving for more than 30 minutes, and returning to continue shopping), he would also count as 2 sessions but only his first session would be new sessions because he is a new user.
Between these 4 total interactions, the new sessions percentage would be 25%.