GA4 Key Events vs Conversions: Why the Numbers Differ

Olamide Sule, founder of Dolphin Analytics: a digital analytics expert based in London, setting up and fixing GA4 and Google Ads tracking for agency and in-house clients.

You open GA4 and see one number of purchases. You open Google Ads and see another, for the same week and the same action. Then someone asks which one the bidding is using, and nobody in the room is sure. We sort out this split for clients most weeks as part of our GA4 setup work, and if you’re pulling your hair out with data challenges like this one, you’re in good company. This is the walkthrough we give them: what each term means, why the counts differ, and how to make sure Google Ads learns from the right action. For the wider fix list, see our conversion tracking service.

What is the difference between a GA4 key event and a conversion?

A GA4 key event is an event you mark as important to your business, so Google Analytics reports it across every channel. A conversion is the action Google Ads measures and optimises campaigns against. Google split the terms because events marked as conversions in Analytics were measured differently from Google Ads conversions, which caused discrepancies between the two products, as its note on the change to key events explains.

In practice, the same form submission or purchase can live in both places under two names. The table sums up Google’s own pages on key events, conversion windows and creating conversions from key events:

	GA4 key event	Google Ads conversion
Where you set it	GA4: Admin, Data display, Events	Google Ads: Goals, Conversions (or created from GA4)
What it’s for	Analysis across all channels	Measuring and bidding on ad performance
Who gets credit	Any channel that drove the visit	Only an ad interaction
Where it shows in GA4	Standard reports	The Advertising section only

Google’s help page on key events confirms that Google Ads conversions don’t appear in standard Google Analytics reports. That’s why a team reading the acquisition reports in GA4 and a PPC manager reading Google Ads can both be right and still disagree.

Why do GA4 key events and Google Ads conversions show different numbers?

GA4 key events and Google Ads conversions differ because each product dates, credits and counts the same action by its own rules. Google Ads ties a conversion to the ad click and only counts actions an ad earned; GA4 counts the key event on the day it happens, whatever the source. Counting methods, windows and reporting lag add smaller gaps on top.

When we audit accounts, the gap is rarely one cause. It’s usually two or three of the reasons below stacked together, so work through all of them before deciding the tracking is broken.

Google Ads dates the conversion to the click

Google Ads’ standard conversion columns are calculated on the time of the click, not the time of the conversion, according to Google’s guide to understanding conversion tracking data. Someone who clicks an ad on Monday and buys on Friday appears in Monday’s Google Ads figures and Friday’s GA4 figures. The same page points to the “by conv. time” columns, which report on when the conversion happened and exist for comparing Google Ads with tools such as Google Analytics.

Only ad-driven actions count in Google Ads

A Google Ads conversion window is the period after an ad interaction during which a conversion is recorded, per Google’s page on conversion windows. No ad interaction means no Google Ads conversion. GA4 still records the key event for a visitor from organic search, email or a direct visit, so GA4 almost always shows the higher total.

The counting methods may not match

GA4 offers two key event counting methods: “once per event”, which counts every time the event fires, and “once per session”, a legacy option that counts it once within a session. Google Ads has its own counting options: “Every”, which counts each conversion after an ad interaction, and “One”, which counts one conversion per ad click. A lead form set to “One” in Google Ads and “once per event” in GA4 will show different counts whenever someone submits twice.

The windows are different lengths

In GA4’s attribution settings, the lookback window defaults to 30 days for acquisition key events and 90 days for all other key events. Google Ads applies a click-through conversion window that defaults to 30 days when not customised, per its conversion windows help page. A long consideration cycle can fall inside one window and outside the other.

Google Ads data arrives later

Google Ads reporting lags can take up to 24 to 48 hours, per Google’s conversion data guide. Comparing yesterday’s figures across the two tools will often show a gap that closes by itself.

The same action is counted twice on the Google Ads side

The fault we find most often has nothing to do with GA4’s rules. An account tracks a purchase with the Google Ads tag and also imports the matching GA4 key event, and both sit in the Conversions column. Google Ads then reports more conversions than GA4 has key events, and bidding learns from an inflated signal. Our post on GA4 duplicate purchase events covers the GA4 side of double counting.

Which one does Google Ads bidding learn from?

Google Ads bids on primary conversion actions, not on GA4 key events directly. Google’s page on primary and secondary conversion actions says primary actions are reported in the Conversions column and used for bidding when their goal is used for bidding. Secondary actions show only in All conversions, for observation.

A GA4 key event therefore affects bidding only once it’s shared with Google Ads as a conversion and set as primary. Google’s guide to creating Google Ads conversions from GA4 key events adds a detail that catches teams out: Google Ads marks a new conversion as secondary when the account already has goals from an Analytics property. So an import can look set up and still teach the bidding nothing.

Our rule of thumb is one source per action. Pick either the Google Ads tag or the GA4 import for each purchase or lead, make that one primary, and keep the other as secondary so you can still compare them. To choose, make the source that fires most reliably on your site the primary one. If you’re unsure whether conversions reach Google Ads at all, start with our guide to Google Ads not tracking conversions.

How do you set up a GA4 key event and share it with Google Ads?

Mark the event as a key event in GA4, then create a Google Ads conversion from it inside GA4. Both steps happen in the GA4 interface, and the second needs the GA4 property linked to Google Ads with auto-tagging switched on, as Google’s conversion creation guide lists under its prerequisites.

1. Mark the key event. In GA4, open Admin, then under Data display click Events, and click the star next to the event, per Google’s key events help page.
2. Set the counting method. On the same key event, choose “once per event” unless you have a reason for the legacy session option.
3. Create the conversion. In GA4, go to Advertising, then Conversion management, click New conversion, choose the Google Ads account, select the key event, and click Save, following the steps in the conversion creation guide.
4. Choose the credited channels. In the same guide, the shared conversion can credit “Google Paid Channels” or “Paid and Organic Channels” for web conversions.
5. Check primary or secondary. In Google Ads, open Goals, then Conversions, find the new action, and confirm whether it’s primary. Set the duplicate source to secondary if both exist.

For the tag-side setup, including how to confirm the event fires before you import it, our Google Ads conversion tracking guide walks through each step.

Do you need Google Tag Manager to create key events?

You don’t need Google Tag Manager when the action is already an event in GA4. GA4’s Create event option, under Admin, then Data display, then Events, builds a new event from an existing one, such as a page_view whose URL is your thank-you page, according to Google’s guide to creating events without code. The same guide says new events can only be based on existing events.

That limit is the dividing line. A thank-you page, a file download or a purchase that already sends an event can become a key event with no code. A button click or form submission that sends nothing to GA4 yet still needs a tag, whether you add it in Google Tag Manager or in the site’s code. Our explainer on GTM vs GA4 covers which tool does what, and how events work in GA4 covers the event model underneath.

How do you reconcile the two numbers?

Compare like with like before you call anything broken. Most of the gap disappears once both tools report on the same date basis, the same counting rule and the same set of actions.

1. Switch Google Ads to “by conv. time”. Add the Conversions (by conv. time) column so both tools date the action the same way, as Google’s conversion data guide suggests for comparisons with Google Analytics.
2. Match the counting methods. Put the GA4 key event and the Google Ads action on equivalent settings: “once per event” in GA4 alongside “Every” in Google Ads, which Google’s counting options page recommends for purchases.
3. Compare against paid traffic only. Set GA4 to show key events from your Google Ads campaigns, not the property total, because Google Ads never counts the organic, email and direct actions GA4 includes.
4. List every primary action. In Google Ads, check that no purchase or lead is counted by two primary actions.
5. Wait out the lag. Compare periods that ended at least two days ago.

If a gap remains after those five checks, the tracking itself is the suspect: a tag firing twice, a consent setup blocking one side, or a key event GA4 never received. Our guide to Google Analytics not tracking conversions covers the GA4 side of that.

When should you call someone?

Call someone when the numbers still disagree after you’ve matched dates, counting and sources, or when you can’t say for certain which action your bidding learns from. Both signs mean the fault sits in the setup, not in the reporting rules, and every week it runs, Google Ads optimises spend on the wrong signal.

Other thresholds we’d treat as the point to stop self-serving: several conversion actions tracking the same purchase, an import that stays secondary however you set it, or GA4 key events that exceed the orders in your store or CRM. We set up and fix GA4 key events and Google Ads conversions for agency and in-house teams, and we’ve done it at scale.

We've set up hundreds of GA4 properties and Tag Manager containers for agency and in-house clients.

That’s the work behind our GA4 setup service. If you’d like a first look at what’s firing on your site, run a free scan with Sonar, our tracking checker. If the split between GA4 and Google Ads is costing you confidence in your bidding, tell us what’s broken, or book a call.