Analytics session: definition, duration and calculation
Updated on February 22, 2026
Quick definition
A session is a period of continuous activity by a user on a website, grouping all the pageviews and interactions performed during a single visit. The session is the fundamental unit of measurement in web analytics, allowing visitor behaviour to be analysed in a grouped and coherent way — distinct from the concept of a unique visitor.
How it works
In web analytics, a session groups all interactions of a single user on a site during a continuous period. In the classic configuration, a session expires after 30 minutes of inactivity or at midnight.
For example, if a user visits your site at 11:50 am, leaves, and returns at 12:05 pm, that constitutes two distinct sessions. Sessions can contain multiple pageviews, events and conversions.
Average session duration is calculated by measuring the gap between the first and last interaction — which raises a methodological issue: if a user visits only one page (bounce), the duration is 0 seconds because there is no second interaction to calculate the gap.
Some modern tools like Sublim use engagement events (scroll, detected inactivity) to measure duration more accurately, even in bounce cases.
The number of sessions is always higher than the number of unique visitors: the same visitor can generate multiple sessions in a day.
Why it matters
Session counting is a fundamental metric for assessing a site's popularity and attractiveness over time.
Analysing sessions helps detect traffic trends, the impact of marketing campaigns and seasonal variations. Segmenting sessions by traffic source, device or geography provides a precise view of traffic quality per channel.
- Session depth (number of pageviews, events triggered) evaluates user engagement
- The sessions / unique visitors ratio indicates the loyalty level
- It is also a key metric for sizing a site's technical infrastructure
How to improve or use it
- 1Work on alignment between your ads or organic results and the content of your landing pages to reduce bounces.
- 2Improve internal navigation with a clear link structure to encourage multi-page exploration.
- 3Use relevant content recommendations (related articles, similar products) to extend session duration.
- 4Analyse sessions by segment to identify the behaviours of the most engaged users and reproduce those conditions.
With Sublim
Sublim calculates sessions with a serverless approach that does not depend on session cookies. Thanks to detection of real activity (scroll, clicks, time on page), Sublim provides session metrics more faithful to real engagement — without requiring user consent to operate, unlike solutions based on third-party cookies.
Frequently asked questions
What is the difference between a session and a unique visitor?
A unique visitor is a distinct person (or device) identified on your site. A session is a visit. A unique visitor can generate multiple sessions: for example, if they visit your site in the morning and again in the evening, that counts as 1 unique visitor but 2 sessions.
How long does a session last by default?
In most analytics tools, the session expires after 30 minutes of inactivity. A new session also starts at midnight or when a user arrives via a new traffic source. These parameters can usually be customised to suit your site's needs.
Why is the number of sessions higher than the number of visitors?
This is entirely normal: a single visitor can visit your site multiple times within the analysed period. Each distinct visit (separated by more than 30 minutes of inactivity or occurring after midnight) is counted as a new session. A sessions/visitors ratio greater than 1 indicates a good level of loyalty or returning visitors.
Related terms
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A unique visitor is a distinct person (or device) identified on a webs…
A segment is a filtered subset of your visitors or sessions, defined b…