Universal Analytics stopped processing data on July 1, 2023. If you’ve migrated to GA4 (or are still figuring it out), understanding the fundamental differences between these platforms is crucial. GA4 isn’t just an upgrade—it’s a completely different approach to analytics.
Here’s everything that changed.
The Core Difference: Data Models
The most significant change is how data is structured and collected.
Universal Analytics: Session-Based Model
UA organized data around sessions and hits. A session was a group of user interactions within a time period, and hits were the individual interactions:
- Pageview hit — User views a page
- Event hit — User clicks something (with Category/Action/Label)
- Transaction hit — User completes a purchase
- Social hit — User interacts with social features
Each hit type had its own schema and limitations. Events were capped at 500 per session.
GA4: Event-Based Model
GA4 treats everything as an event. There are no hit types—just events with parameters:
page_view— User views a page (event)click— User clicks something (event)purchase— User completes a purchase (event)
Every event can have up to 25 custom parameters. This flexibility is powerful but requires rethinking how you structure tracking.
Key implication: In UA, a pageview and an event were fundamentally different. In GA4, they’re the same thing—just events with different names and parameters.
Metrics: What Changed
Several familiar metrics work differently or were replaced entirely.
Bounce Rate → Engagement Rate
UA’s bounce rate measured single-page sessions (user left without interaction). This was problematic—a user who read an entire article and left was counted the same as someone who left immediately.
GA4 replaced this with engagement rate:
- An “engaged session” lasts 10+ seconds, OR has a conversion, OR has 2+ page views
- Engagement rate = engaged sessions ÷ total sessions
Bounce rate still exists in GA4 but is calculated as the inverse (100% - engagement rate).
Sessions
Sessions work similarly but with key differences:
- UA: New session after 30 minutes of inactivity, or at midnight, or on new campaign parameters
- GA4: New session only after 30 minutes of inactivity (no midnight reset, no campaign reset)
This means GA4 typically reports fewer sessions than UA did for the same traffic.
Users
UA had “Total Users” (anyone who visited) and “New Users.”
GA4 uses:
- Active Users — The primary user metric (users with engaged sessions)
- Total Users — Anyone who triggered an event
- New Users — First-time users
When you see “Users” in GA4 reports, it’s Active Users by default—which is lower than UA’s Total Users for the same traffic.
Conversion Rate
UA calculated conversion rate as: conversions ÷ sessions
GA4 calculates it as: conversions ÷ users (or sessions, depending on the report)
This change alone can make your conversion rates look dramatically different.
Reports: Complete Redesign
GA4’s reporting interface is completely different from UA.
What’s Gone
These UA reports don’t exist in GA4’s standard interface:
- Behavior Flow — Replaced by path exploration
- Site Content → All Pages — Now in Engagement → Pages and Screens
- Multi-Channel Funnels — Replaced by Attribution reports
- Custom Reports — Replaced by Explorations
- Treemaps, Motion Charts — Removed
What’s New
GA4 added:
- Explorations — Flexible analysis workspace for custom reports
- Path Exploration — Visual user journey analysis
- Funnel Exploration — Flexible funnel building
- Segment Overlap — Compare audience segments
- User Lifetime — LTV and retention analysis
Report Navigation
| UA Location | GA4 Location |
|---|---|
| Audience → Overview | Reports → User → User attributes |
| Acquisition → All Traffic | Reports → Acquisition → Traffic acquisition |
| Behavior → Site Content | Reports → Engagement → Pages and screens |
| Conversions → Goals | Reports → Engagement → Conversions |
| Conversions → Ecommerce | Reports → Monetization → Ecommerce purchases |
Goals vs. Conversions
UA had “Goals” (up to 20 per view). GA4 has “Conversions” (up to 30 per property).
UA Goals
- Defined in Admin for each View
- Types: Destination, Duration, Pages/Session, Event
- Couldn’t be changed without affecting historical data
GA4 Conversions
- Any event can be marked as a conversion (toggle on/off)
- No goal types—just events
- Can mark/unmark without affecting historical data
- Automatically includes
purchaseas a conversion
Migration tip: If you had destination goals (thank-you page visits), create equivalent page_view events with a condition in GTM, or use GA4’s “Modify and create events” feature.
Views vs. Data Streams
UA used Views to filter data into separate reports. You might have had an “All Traffic” view, a “Filtered (no internal)” view, and a “Test” view.
GA4 uses Data Streams instead—but they serve a different purpose. A data stream is a source of data (web, iOS, Android), not a filter.
For filtering in GA4:
- Use Data Filters (Admin → Data Settings → Data Filters)
- Create separate properties if you need truly separate data
- Use comparisons in reports for ad-hoc filtering
Attribution Models
UA defaulted to last-click attribution. GA4 defaults to data-driven attribution.
UA Attribution
- Last Non-Direct Click (default)
- Last Click
- First Click
- Linear
- Time Decay
- Position Based
Model comparison required the Multi-Channel Funnels reports.
GA4 Attribution
- Data-Driven (default, uses machine learning)
- Last Click (cross-channel or ads-preferred)
- First Click
GA4 applies attribution at the property level, not just in specific reports. This affects all your conversion reporting.
Data Retention
A critical operational difference:
- UA: Free accounts retained detailed data for 26 months
- GA4: Free accounts retain user-level data for 2 or 14 months (your choice)
If you need longer retention, you must export to BigQuery.
BigQuery Integration
This is where GA4 significantly improves on UA.
- UA: BigQuery export was GA360-only ($$$$)
- GA4: BigQuery export is free for all accounts
With BigQuery export, you get:
- Raw, hit-level (event-level) data
- Unlimited retention
- SQL access for custom analysis
- ML capabilities
If you’re doing serious analysis, BigQuery export is essential.
What Stayed the Same
Despite all the changes, some concepts carry over:
- Session timeout (30 minutes default)
- Campaign tracking via UTMs
- Filters for internal traffic
- Real-time reports
- Google Ads integration
- Search Console integration
Migration Considerations
If you’re still reconciling your UA and GA4 data:
Why Numbers Don’t Match
UA and GA4 will never show identical numbers because:
- Different user counting (Total vs Active)
- Different session definitions
- Different attribution models
- Different event schemas
- Sampling differences at high volumes
Don’t try to make them match—just understand why they differ.
What to Preserve from UA
Before UA data is completely inaccessible:
- Export key reports to CSV/PDF
- Save custom report configurations (recreate in GA4 Explorations)
- Document your goal configurations
- Note any custom dimensions/metrics
- Export to BigQuery if available
GA4 Setup Checklist
Ensure your GA4 is properly configured:
- Enhanced measurement enabled
- Conversions marked for key events
- Data retention set to 14 months
- Internal traffic filtered
- Cross-domain tracking configured (if needed)
- BigQuery export enabled
- Google Ads linked
- Search Console linked
The Bottom Line
GA4 isn’t better or worse than UA—it’s different. The event-based model is more flexible, BigQuery integration is powerful, and engagement metrics are more meaningful than bounce rate.
The learning curve is real, but the platform is capable once you understand how it thinks about data.
Get a free scan if you’re unsure whether your GA4 setup is capturing the data you need. We’ll show you what’s working and what’s missing.