InsightGA4AttributionLead reporting
GA4 vs. last-click: why your best lead sources look broken in the default report
GA4's default acquisition report buries the channels that actually start conversations. Here is how to diagnose what your reports are hiding before you cut a budget line.
Main takeaway
GA4's data-driven model and its summary reports are not the same thing. The default acquisition table shows last-click session data, not the model's output.
Best for
Service businesses running paid and organic traffic together
Time to ship
2 to 3 hours
Plan for a credible first pass
Recommended next step
Campaign ROI check
Check your cost and conversion assumptions before your next budget call.
On this page
Why this matters
GA4's default Traffic acquisition report uses last-click attribution and ignores the data-driven model GA4 actually applies to key events. The result: top-of-funnel channels that warm leads (organic search, referrals, display) get little or no credit in the report most teams read for budget decisions. To see the full picture, compare models in the Attribution models report in GA4's Advertising section and check that your lookback window covers your sales cycle.
The cost of skipping that diagnosis is real. Service businesses running annual budget reviews right now are looking at a full year of GA4 data. Read that data at face value and the channels doing early-stage work get cut. Lead volume drops three to six months later, and the team has no clear reason why.
Last-click vs. data-driven attribution at a glance
| Aspect | Last-click attribution | Data-driven attribution |
|---|---|---|
| Where to find it in GA4 | Reports > Acquisition > Traffic acquisition | Advertising > Attribution models report |
| How credit is assigned | 100% to the final source before conversion | Distributed across touchpoints based on observed conversion patterns |
| Best for | Reading final-click channel volume | Identifying under-credited top-of-funnel channels |
| Limitation | Erases the role of awareness channels | Has little of your own data to learn from when a key event gets only a few completions a month |
| Default in GA4 | Always, in session-scoped reports like Traffic acquisition | Yes, as the reporting model for key event credit in event-scoped reports and explorations |
Framework
The attribution diagnosis framework
1) Identify which report you are actually reading (10 minutes)
Open GA4 and go to Reports > Acquisition > Traffic acquisition. The channel column here uses session-scoped last-click attribution by default. This is not the same as the data-driven model GA4 applies to key events in the Advertising section and in explorations. Write down which report you have been relying on for budget decisions. If it is the Traffic acquisition table, you have been reading last-click data regardless of what your GA4 attribution setting says.
2) Pull the Attribution models report (20 minutes)
Open the Attribution models report in the Advertising section (older guides call it Model comparison). The Advertising section's reports require linking the property to Google Ads or another Google advertising product. The report sums all key events by default, so select your primary lead event, form submissions or calls, and compare Paid and organic last click against Data-driven side by side. Check the % change column for each channel. Any channel where data-driven assigns materially more credit than last-click is a channel your budget decisions have been undervaluing.
3) Check your key event setup (15 minutes)
A model comparison is only as good as the events feeding it. Go to Admin > Data display > Events and confirm that your key lead events, contact form submissions, phone click events, booking completions, are marked as key events, GA4's name for conversions since 2024. Marking an event only counts data from that point forward and doesn't change history. Data-driven attribution builds a separate model for each key event, so what matters is steady volume on your main lead event, not how many events you mark.
4) Review the Attribution paths report (20 minutes)
Open the Attribution paths report in the Advertising section (older guides call it Conversion paths). Select your top lead key event. Look at the "paths" column for multi-step sequences. If most paths show only one touchpoint, either your tracking has gaps, users are converting on their first visit, or cross-device journeys are breaking the session chain. Note which channels appear most often as first touch and which appear most often as last touch. A channel that consistently appears first but rarely last is a candidate for under-credit in any last-click view.
5) Audit your lookback window (10 minutes)
GA4's default attribution lookback window is 90 days for lead-type key events, and 90 days is also the maximum (only acquisition key events like first visits default to 30). For service businesses with longer consideration cycles, a roofing job, a legal matter, a home renovation, a window someone shortened to 30 or 60 days may cut off early touchpoints entirely. Go to Admin > Data display > Events, open the attribution settings, and check the window. If it is below 90 days and your average time from first visit to lead submission is longer, set it back to 90 days and note the date you made the change so you can compare before and after, since the change only applies going forward.
6) Cross-reference against a non-GA4 source (15 minutes)
GA4 will always have gaps because it runs in the browser and is subject to ad blockers, consent mode restrictions, and session fragmentation. Pull your CRM or form tool's raw submission log for the same date range. Compare total lead count to GA4's key event count for the same event. A gap larger than 15 to 20 percent suggests tracking issues that will distort any attribution model, regardless of which one you use.
Scorecard
Scoring worksheet
8Total points
possible
- Conversion events set up correctly and marked in GA40 to 2
- Model comparison report reviewed in the last 30 days0 to 1
- Lookback window matched to your actual sales cycle0 to 1
- Conversion path report showing multi-touch paths for at least some leads0 to 2
- GA4 lead count within 20 percent of CRM or form tool count0 to 2
Action plan
This week action plan
- Day 1
Run steps 1 and 2. Write down which channels show the largest gap between last-click and data-driven.
- Day 2
Audit conversion events in GA4 Admin. Fix any that are missing or misfiring.
- Day 3
Pull the conversion path report and note first-touch vs. last-touch channel patterns.
- Day 4
Check and adjust the lookback window if needed. Log the change date.
- Day 5
Pull your CRM lead count for the last 90 days and compare to GA4 conversion volume. Document the gap.
Avoid these
Common mistakes
- Reading the Traffic acquisition table and assuming it reflects GA4's attribution model, when it reflects last-click session data.
- Running a model comparison on a lead event with only a handful of completions a month, which gives the data-driven model little of your own data to learn from.
- Adjusting channel budgets immediately after setting up GA4 or a new key event, without waiting for enough key event history to build up (marking an event only counts data from that point forward).
Common questions
Frequently asked questions
Google has not published a minimum volume for GA4's data-driven model. Its documentation says each model is built for a specific key event and, depending on data availability, may lean on aggregate data from GA4's data sharing settings. A service business logging only a handful of leads a month from a given event gives the model little of its own data to learn from. At that volume, the attribution paths report and a manual CRM cross-reference will give you more useful signal than the model comparison.
Not directly, and only if you exported your UA data, since Google removed access to Universal Analytics data starting the week of July 1, 2024. UA used session-based attribution throughout. GA4 uses event-based tracking and a different default model. Channel groupings also changed, so organic social in UA may be split or recategorized in GA4. Year-over-year comparisons that cross the migration date should be treated as directional at best. For annual reviews covering the migration window, note the discontinuity explicitly and lean on absolute lead volume from your CRM rather than GA4 channel percentages.
For most service businesses, the answer is no. Data-driven is the most defensible default because it uses your actual conversion data rather than a fixed rule. The more useful change is making sure you are reading the right report, the Attribution models report in the Advertising section, rather than the Traffic acquisition table, which always shows last-click regardless of your settings. Linear is no longer an option: GA4 retired it, along with first click, time decay, and position-based, in November 2023. The remaining alternatives, Paid and organic last click and Google paid channels last click, give 100% of the credit to one last click, so at low volume lean on the attribution paths report and your CRM instead of switching models.
Put this into practice
Turn this insight into a ranked homepage action list
Check your cost and conversion assumptions before your next budget call.