GA4 Conversion Tracking: Key Events, Custom Conversions, and What Changed From UA

Universal Analytics had goals. You pointed them at a URL, an event, or a duration threshold and they counted conversions. GA4 replaced goals with key events, changed how conversions are counted, and added enough flexibility that most teams either overconfigure or underconfigure the whole thing.

The result: many GA4 properties still have no key events configured, or they have page_view marked as a key event (which makes every session a "conversion"), or they have three different events tracking the same form submission because nobody cleaned up after migration.

What changed from UA to GA4

The shift from Universal Analytics to GA4 changed three things that matter for conversion tracking.

The naming shift. UA called them "goals." GA4 called them "conversions" for two years, then renamed them key events in March 2024 to distinguish them from Google Ads conversions. Key events are GA4's concept: events you flag as important for your reports. Google Ads conversions are the actions Google Ads optimizes toward. A GA4 key event becomes a Google Ads conversion only when you explicitly import it.

The counting change. UA counted each goal once per session. A visitor who submitted the same form three times in one session got one goal completion. GA4 defaults to counting every event fire: three submissions equal three key events. GA4 added a "once per session" option, but the default is "every event." If you migrated without adjusting this, your conversion count inflated overnight.

The configuration change. UA goals were configured in the admin panel. GA4 key events require the event to exist first. You cannot create a key event for an event that has not fired. The workflow is: make the event fire (via enhanced measurement, GTM, or custom code), wait for it to appear in GA4's event list, then mark it as a key event in Admin > Data display > Key events. This three-step process is why so many properties have no key events at all.

Setting up key events correctly

Lead generation sites. The primary key event is form submission. You have three approaches: enhanced measurement's built-in form_submit (fires on every form, including search and login forms, so it is often too broad), a custom event via GTM (precise control, testable in DebugView, supports custom parameters), or GA4's event modification rules (creates a new event from an existing one with conditions, no GTM changes needed). For most setups, the GTM approach is best because it is the most flexible and testable.

E-commerce sites. Mark purchase as a key event. Do not also mark add_to_cart, begin_checkout, and view_item as key events. They are useful as funnel steps, but marking every step as a key event inflates your count and confuses Smart Bidding if you import to Google Ads.

Content sites. Consider a newsletter signup confirmation, an engaged article read (scrolled to 75% and spent more than 60 seconds), or outbound clicks to partner or sponsor links. Choose one primary key event that represents the business objective. Track everything else as regular events.

Importing key events to Google Ads

Marking an event as a key event in GA4 does not automatically send it to Google Ads. You must import it through Google Ads under Goals > Conversions > New conversion action > Import > Google Analytics 4 properties.

When importing, set each action as Primary (used for bidding) or Secondary (observed only). If you import five key events as Primary, Smart Bidding tries to maximize all five simultaneously, which dilutes the signal. Import one Primary conversion that represents business value and set the rest as Secondary.

Imported conversions take up to 24 hours to sync. GA4 uses data-driven attribution across all channels; Google Ads uses its own attribution scoped to Google's ad network. The same event can have different conversion credit in each system. This is expected, not an error. Document the expected discrepancy in your report methodology. For a deeper look at why these numbers diverge, see our guide on GA4 vs Google Ads data discrepancies.

Common mistakes that corrupt your data

Marking page_view as a key event. If page_view is a key event, every session that includes a page view is a "conversion." Your conversion rate becomes roughly 100%. Smart Bidding optimizes for page views instead of business outcomes. Check every property's key event list during onboarding.

Too many key events. A property with eight key events is tracking eight different actions as conversions. The aggregate number becomes meaningless. Keep key events to one to three per property: one primary business outcome and optionally one secondary signal.

Not setting the counting method. The default is "every event." For lead generation forms, a visitor who hits submit, gets an error, and hits submit again counts as two conversions. Switch lead-gen key events to "once per session" counting.

Not testing after changes. After any conversion tracking change, submit a test conversion, verify it in DebugView, wait 24 hours, check the key events report, and check Google Ads conversion reporting if imported. Five minutes of verification prevents months of wrong data.

Keeping conversion data reliable over time

Key event configuration is not a set-and-forget task. CMS updates can break form tracking, GTM changes can introduce duplicate tags, and team members may add new key events without understanding the consequences. A monthly check of your key event list, counting methods, and event fire rates catches drift before it corrupts a full reporting period.

SyncingBeam pulls key event counts daily through the GA4 Data API. Because the daily pull stores conversion data at daily grain, you can spot changes in event volume the day they happen rather than discovering two weeks later that a form tag broke. When a key event's daily count drops to zero or spikes beyond its normal range, the anomaly surfaces before anyone opens a report.