Google Analytics 4 (GA4) is Google’s current web and app analytics platform, replacing Universal Analytics. Universal Analytics was shut down in 2023 — GA4 is now the only standard.
What sets GA4 apart is that its data model is event-based from the ground up. Nearly every user action, including page views, is recorded as an event; the concept of a session is built on top of these events afterward.
The GA4 automatically collected events documentation states that events like page_view, session_start, first_visit, and user_engagement are collected automatically with no additional setup required. The key events documentation defines a “key event” (formerly called a conversion) as an event that measures an action of particular importance to the business’s success.
Why Is GA4’s Data Model Different?
Where Universal Analytics thought in terms of sessions, GA4 treats everything as an event. Even a page view is now an event called page_view.
Core events collected automatically
page_view fires every time a page loads or the browser history changes. session_start creates an automatic session ID when a user arrives on the site. first_visit is recorded on a user’s first visit, and user_engagement when the page stays in focus for at least one second.
Enhanced Measurement collects data without any code
With Enhanced Measurement turned on, link clicks, file downloads, video engagement, and form submissions can all be captured automatically without any additional setup — which is why, if it’s off, turning it on is usually the first thing worth checking.
How Do You Mark a Key Event?
In GA4, the term “conversion” is now officially called a “key event.” Any event considered valuable to the business can be marked as a key event.
Not every event should be a key event
A page view is an event, but for most businesses it isn’t, on its own, a meaningful outcome. Events closer to a real business result, like form submissions or purchases, should be the ones marked as key events. For example, on a B2B site, “Contact page view” and “Contact form submission” carry different value; marking only the former as a key event can misleadingly present visitors who never filled out a form as “conversions” too.
This is where the Google Ads connection happens
GA4 events marked as key events can be used to create Google Ads conversions. This connection provides consistent conversion counting and remarketing audience creation between Ads and Analytics. See What Is Conversion Tracking? for more detail.
How Do You Read the Core Reports?
GA4’s report structure runs along a few main axes: acquisition, engagement, monetization, and free-form exploration.
The acquisition report shows channel performance
This report shows which channel (organic search, paid ads, social media) traffic is coming from. Channel-level budget decisions usually start with this report.
Exploration reports are used for custom analysis
Outside the standard reports, when you need funnel- or segment-based custom analysis, the Explorations section is used. These reports are directly affected by the data retention setting.
What Does Data Retention Period Affect?
User-level data retention can be set to 2 months or 14 months.
This setting doesn’t affect standard reports
The GA4 data retention documentation states that this setting doesn’t affect standard aggregated reports — it only affects Exploration reports and funnel analyses. Once the period expires, data is automatically deleted monthly.
14 months is generally the safer starting point
A short retention period can shut down the ability to run historical funnel or segment analysis earlier than you’d like. Unless there’s a specific reason not to, the 14-month period leaves a more flexible analysis window.
Pre-Launch Check
When evaluating a GA4 setup:
- Is Enhanced Measurement on, and are basic interactions being collected automatically?
- Have the events that matter to the business been marked as key events?
- Does the data retention period match the depth of analysis you need?
- Is the Google Ads link set up, with key events being shared as conversions?
Common Mistakes
The most common mistake is marking every event as a key event. In that case, the report gets bloated, and the action that’s genuinely valuable can get lost among more frequent but less valuable events.
The second mistake is carrying over Universal Analytics’ old conversion definitions to GA4 without questioning them. GA4’s event-based model calculates some legacy metrics differently (like pageviews per session); comparing the old report directly against the new one can show a difference even without any real change in performance.
Summary
GA4 works on an event-centric data model, not a session-centric one. Core events are collected automatically, and the ones that matter to the business are additionally marked as key events. The data retention setting only affects Exploration reports; standard reports aren’t limited by it.