In early 2024, GA4's "Mark as conversion" toggle became "Mark as key event." Many users assumed the change was cosmetic and moved on. It wasn't. 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 it, your mental model of "conversion" in each platform is probably wrong.
This guide covers what changed, why, and what 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 Admin (a destination URL, a session duration threshold, a specific event) and UA counted a completion whenever the conditions were met. Goals were also what you imported into Google Ads, 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 the event, and it showed up in the Conversions report and could be imported into Ads. Clean and flexible, but it set up the terminology confusion that followed.
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. They appear in your GA4 reports, drive the key event rate metrics, and are the raw material for conversion tracking. Marking one has no effect on your Google Ads campaigns.
- Conversions (the new meaning): key events explicitly imported into Google Ads. Only these count as conversions in Ads bidding, Smart Bidding optimisation, and the Campaigns interface.
Warning: From 2024, "Conversions" refers specifically to key events imported into Google Ads. A "Conversions" column in Google Ads and a "Key events" count in GA4 for the same action measure 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
The table maps the terminology across four states: Universal Analytics, GA4 before 2024, GA4 after 2024, and what "conversions" now means in Ads.
| 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" on an event in Admin > Events | Toggle "Mark as key event" on an event in Admin > Events | Import the key event into Ads via the Ads & attribution link, or mirror it with an Ads conversion action |
| Where it appears | UA Goals reports; importable into Ads | GA4 Conversions report; importable into Ads | Key events in GA4 Engagement reports; key event rates in standard reports | Conversions column in Ads campaign, ad group and keyword reports |
| Effect on Google Ads | Drives Smart Bidding and conversion columns when imported | Drives Smart Bidding and conversion columns when imported | None directly. Smart Bidding ignores key events until imported as conversions | Feeds Smart Bidding (Target CPA, Target ROAS, Maximise Conversions) and 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 events / sessions (session-scoped) or / users (user-scoped); see event scopes | Ads conversion rate = conversions / clicks, calculated in Ads, not GA4 |
| Historical data impact | Non-retroactive: counted from the date the goal was created | Retroactive: toggling an event back-filled historical data | Retroactive: marking an event back-fills its historical data | Not retroactive: Ads counts from the date you activate the import |
Why Google made the change
Google had a reason for the rename. Before 2024, "conversion" meant subtly different things in GA4 and Google Ads. In GA4, it was an important event you wanted to track. In Ads, it had 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), so Smart Bidding optimised for the wrong signals.
By calling on-site tracking "key events" and reserving "conversions" for Ads-linked actions, Google made the distinction explicit in the UI, to stop analysts 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
The conversion rate metrics in your GA4 standard reports changed labels. What was a "session conversion rate" is now a "key event rate." The formula is the same (key events divided by sessions); only the label changed.
There are two key event rate metrics:
- Session key event rate: the percentage of sessions in which the key event fired at least once. It is the closest equivalent to the old session conversion rate and the right metric for evaluating landing pages and traffic channels. See event scopes for why it differs from raw key event counts.
- User key event rate: the percentage of users who triggered the key event at least once in the period. More useful for retention analysis than campaign performance.
In Google Ads, conversion rate is conversions divided by ad clicks, calculated entirely within Ads 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 do not contradict each other: they have different denominators and attribution windows. Your attribution model settings affect both, but in different ways.
The impact on historical reporting
The rename did not alter any historical data. Events marked as conversions in GA4 before 2024 were carried over automatically as key events; only the label changed. Your trend lines and historical counts were preserved.
There is a subtler issue. Before the rename, some teams imported many GA4 "conversions" into Google Ads indiscriminately, because the shared label made both feel equivalent. After it, Google recommended auditing your Ads conversion actions and removing micro-conversions that inflated counts. If you or a previous analyst did that in 2024, your historical Ads conversion numbers will show a drop that reflects the audit, not 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 moved from UA to GA4 and set up conversions before 2024, work through this checklist:
- Audit your key events. In GA4, go to Admin > Data display > Key events. List every event currently marked and ask: is this a meaningful business outcome, or 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. The guide on the Ads–GA4 connection shows how to do this safely.
- Do not re-import everything. You do not need an Ads conversion action for every key event. Key events that exist purely for on-site analysis (scroll depth, video plays, PDF downloads) should never be imported into Ads.
- Check your Smart Bidding signals. If you cleaned up Ads conversion actions, Smart Bidding may have lost signals it used. Allow campaigns a 2–4 week learning period and watch cost per conversion rather than raw conversion volume.
- Update your reporting language. Change "GA4 conversions" to "key events" in dashboards and client reports, especially those that also include Ads data, where "conversions" now means something different.
- Verify your conversion rate metrics. Confirm whether reports show 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.
Properties created after the rename
If you created your GA4 property after the rename, you never saw the old "Mark as conversion" toggle. For you, this is simply how GA4 works: key events for on-site tracking, conversions for Ads optimisation. The distinction still matters (resist importing every key event into Ads), but you have no migration burden. The main thing to understand is why "conversion" appears in both GA4 and Google Ads yet refers to different data, which the table above explains. For how parameters on your events feed into key event tracking, see GA4 event parameters.
Summary
Google's 2024 rename formalised a 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 reporting language probably need a review. Start with the checklist above. The same audit is your chance to tighten the signals Smart Bidding optimises for.