In early 2024, a toggle that had said "Mark as conversion" in Google Analytics 4 quietly changed to "Mark as key event." Many GA4 users saw the update, assumed it was cosmetic, and moved on. It was not cosmetic. The rename was the visible part of a larger restructuring of how GA4 and Google Ads use the word "conversion" — and if you set up your GA4 property before that change, your mental model of what a "conversion" means in each platform is probably wrong.
This guide untangles it: what changed, why, and exactly what you need to do if you migrated from Universal Analytics or configured GA4 before 2024.
The old model: Universal Analytics conversions
In Universal Analytics, a "goal" was the unit of conversion tracking. You created goals in the Admin panel — a destination URL, a session duration threshold, a specific event — and UA would count a goal completion whenever those conditions were met. Goals were also what you imported into Google Ads to track campaign performance. The whole system revolved around goals as the single concept linking on-site behaviour to ad spend.
When GA4 launched, Google replaced goals with a simpler idea: any event could be flagged as a conversion. You toggled a switch next to any event in GA4, and that event would show up in the Conversions report and could be imported into Ads. Clean, flexible — but it set up the terminology confusion that came later.
What changed in 2024
Google split the old "conversion" concept in GA4 into two distinct things:
- Key events — events you have flagged as important in GA4. These appear in your GA4 reports, drive the key event rate metrics in standard reports, and are the raw material for conversion tracking. Marking an event as a key event has no effect whatsoever on your Google Ads campaigns.
- Conversions (the new meaning) — key events that have been explicitly imported into Google Ads. Only these count as conversions in Ads bidding, Smart Bidding optimisation, and the Campaigns interface.
Warning: What GA4 calls "Conversions" in 2024 and later refers specifically to key events that have been imported into Google Ads. If you see a "Conversions" column in Google Ads and a "Key events" count in GA4 for the same action, they are measuring the same underlying event — but the Ads number is filtered to sessions attributable to your campaigns. Do not assume a discrepancy means something is broken.
Before and after: a comparison
The table below maps the full terminology history across four states: Universal Analytics, GA4 before 2024, GA4 after 2024, and what "conversions" now means in the Ads context.
| Concept | UA Goals | GA4 "Conversions" (pre-2024) | GA4 Key Events (post-2024) | GA4 "Conversions" (post-2024, Ads-linked) |
|---|---|---|---|---|
| What you configure | Create a Goal in Admin (destination, duration, event, or pages/visit) | Toggle "Mark as conversion" next to any event in Admin > Events | Toggle "Mark as key event" next to any event in Admin > Events | Import the key event into Google Ads via the Ads & attribution link, or create a conversion action in Ads that mirrors it |
| Where it appears | Goals reports in UA; importable into Ads as a conversion action | Conversions report in GA4; importable into Ads | Key events section in GA4 Engagement reports; key event rate metrics throughout standard reports | Conversions column in Google Ads campaigns, ad groups, and keyword reports |
| Effect on Google Ads | Drives Smart Bidding and is included in Ads conversion columns when imported | Drives Smart Bidding and conversion columns when imported into Ads | No direct effect on Ads. Smart Bidding does not see key events until they are imported as conversions | Directly feeds Smart Bidding (Target CPA, Target ROAS, Maximise Conversions). Counts in the Conversions column |
| Conversion rate calculation | Goal conversion rate = goal completions / sessions | Session conversion rate = converting sessions / sessions; event conversion rate = conversions / events | Key event rate = key event count / sessions (session-scoped) or / users (user-scoped); see event scopes | Ads conversion rate = conversions / clicks, calculated within the Ads interface, not in GA4 |
| Historical data impact | UA goals are non-retroactive — only counted from the date the goal was created | GA4 conversions were retroactive — toggling an event as a conversion back-filled historical data | Key events are retroactive — marking an event back-fills all historical data for that event | No retroactive effect on Ads data — Ads counts conversions from the date you activate the import |
Why Google made the change
The rename was not arbitrary. Before 2024, it was genuinely confusing that the word "conversion" meant subtly different things depending on whether you were looking at GA4 or Google Ads. In GA4, a "conversion" was simply an important event you wanted to track. In Ads, a "conversion" was something with direct monetary implications — it determined how Smart Bidding allocated your budget. Conflating the two led analysts to import GA4 events into Ads that should never have influenced bidding (micro-conversions like scroll depth or video plays, for example), which caused Smart Bidding to optimise for the wrong signals.
By calling on-site tracking "key events" and reserving "conversions" exclusively for Ads-linked actions, Google made the distinction explicit in the UI. The intent was to stop analysts from accidentally feeding junk signals to Smart Bidding.
"Mark as key event" tells GA4 to track this carefully. "Import to Ads" tells Google Ads to optimise for it. These are separate decisions and should be made separately.
How conversion rates are now calculated
One practical consequence of the rename is that the conversion rate metrics in your GA4 standard reports have changed labels. What was previously a "session conversion rate" for a conversion event is now a "key event rate." The formula is the same — key event count divided by sessions — but the label changed.
There are two key event rate metrics to understand:
- Session key event rate — the percentage of sessions in which the key event fired at least once. This is the closest equivalent to the old session conversion rate and is the right metric for evaluating landing pages and traffic channels. See the full explanation of event scopes for why this differs from raw key event counts.
- User key event rate — the percentage of users who triggered the key event at least once during the reporting period. More useful for retention analysis than campaign performance.
In Google Ads, conversion rate is calculated differently: it is conversions divided by ad clicks, and it is calculated entirely within the Ads interface using the imported conversion actions. A GA4 key event rate of 3.2% and a Google Ads conversion rate of 4.8% for nominally the same event are not contradicting each other — they have different denominators and different attribution windows. Your attribution model settings affect both, but in different ways.
The impact on historical reporting
The rename itself did not wipe or alter any historical data. If you had events marked as conversions in GA4 before 2024, they were automatically carried over as key events — the toggle just changed label. Your trend lines and historical counts were preserved.
However, there is a subtler historical issue. Before the rename, some teams had imported many GA4 "conversions" into Google Ads indiscriminately, because the shared label made both feel equivalent. After the rename, Google recommended auditing your Ads conversion actions and removing micro-conversions that were inflating conversion counts. If you or a previous analyst cleaned up those Ads conversion actions in 2024, your historical Ads conversion numbers will show a drop that reflects the audit, not a change in actual business performance. Check your Google Ads change history if you see an unexplained dip around early 2024.
What to do if you migrated from Universal Analytics
If you transitioned from UA to GA4 and set up GA4 conversions during the pre-2024 era, work through this checklist:
- Audit your key events. In GA4, go to Admin > Data display > Key events. List every event currently marked. For each one, ask: does this represent a meaningful business outcome, or is it a micro-conversion that inflates counts?
- Audit your Ads conversion actions. In Google Ads, go to Goals > Conversions > Summary. Check which GA4-sourced actions are set to "Include in Conversions" (the setting that feeds Smart Bidding). Remove or set to "Observation only" anything that is not a genuine bottom-of-funnel action. See the full guide on the Ads–GA4 connection for how to do this safely.
- Do not re-import everything. You do not need an Ads conversion action for every GA4 key event. Key events that exist purely for on-site analysis — scroll depth, video plays, PDF downloads — should stay as key events and never be imported into Ads.
- Check your Smart Bidding signals. If you cleaned up Ads conversion actions, Smart Bidding may have lost some of the signals it was previously using. Give campaigns 2–4 weeks of a learning period and monitor cost per conversion rather than raw conversion volume during that time.
- Update your reporting language. Any dashboards or client reports that refer to "GA4 conversions" should be updated to "key events" to avoid confusion, especially if those reports also include Ads data where "conversions" now has a different meaning.
- Verify your conversion rate metrics. Confirm whether your reports are showing session key event rate, user key event rate, or Ads conversion rate. Label them explicitly — "session key event rate (GA4)" and "conversion rate (Google Ads)" — so stakeholders do not conflate them.
A note on properties created after the rename
If you created your GA4 property after the rename rolled out, you have never seen the old "Mark as conversion" toggle. For you, the current model is simply how GA4 works: key events for on-site tracking, conversions for Ads optimisation. The conceptual distinction still matters — resist the temptation to import every key event into Ads — but you do not have a migration burden to manage. The main thing to understand is why the word "conversion" appears in both GA4 and Google Ads yet refers to different populations of data, which the table above explains. For a deeper look at how parameters attached to your events feed into key event tracking, see the guide on GA4 event parameters.
Summary
Google's 2024 rename was not cosmetic. It formalised a meaningful distinction: key events are what you track in GA4, conversions are what you optimise in Google Ads. The two overlap only when you deliberately import a key event into Ads. If you set up GA4 before the rename, your data is intact — but your Ads conversion actions and your reporting language probably need a review. Start with the checklist above, and treat the audit as an opportunity to tighten your Smart Bidding signals rather than just a housekeeping task.