Cohort
Definition
A group of users who share a common characteristic over a time period. Cohort analysis tracks how groups behave over time.
What is a Cohort?
A cohort is a group of users who share a common starting point or characteristic, tracked over time. The most common is an acquisition cohort – users grouped by when they first visited your site.
For example, everyone who first visited in January 2024 is one cohort. You can then track what percentage of that cohort returned in February, March, and beyond.
Cohort vs Segment
Both group users, but differently:
- Segments filter data by characteristics at a point in time
- Cohorts track the same group over time
A segment might show "returning visitors this month." A cohort shows "visitors who first arrived in January, and how many returned each month after."
Why Cohort Analysis Matters
Cohort analysis reveals retention patterns that aggregate data hides. You might see traffic growing overall, but cohort analysis could show that each new group returns less than the previous one – a warning sign.
What Cohorts Reveal
- Retention: Are people coming back?
- Lifetime value: How much do customers from different periods spend over time?
- Product changes: Did last month's update improve retention?
- Marketing effectiveness: Do certain campaigns bring users who stick around?
Using Cohort Analysis
E-commerce
Track repeat purchases. Do customers acquired during sales events have lower lifetime value than regular customers?
SaaS
Monitor user retention. What percentage of users who signed up in week 1 are still active in week 8?
Content Sites
Measure return visits. Which acquisition channels bring readers who become regular visitors?
Cohort Analysis in GA4
GA4 includes a built-in Cohort Exploration that tracks user retention over daily, weekly, or monthly periods. It's particularly useful for understanding whether improvements to your site are working.