A key event is an event in Google Analytics 4 that you have marked as important to your business, such as a purchase, a submitted enquiry form or a booked consultation. GA4 called these conversions until March 2024, when Google renamed them so that the word “conversion” could mean the same thing in GA4 as it does in Google Ads.
How a key event works
GA4 records activity as events: page views, scrolls, clicks, form submissions and anything else you set up. Marking one as a key event does not change how it is collected. It tells GA4 to count that event as an outcome, so it appears in the key events and key event rate columns across your reports and in the attribution reports in the Advertising section.
At the time of writing (October 2026), you mark an event under Admin, then Data display, then Events or Key events. A few settings are worth knowing:
- Counting method. Once per event counts every occurrence; once per session counts it at most once in a visit. For lead forms, once per session stops a double submission from looking like two enquiries.
- Value. Purchases normally send their own value. For leads you can send a value with the event, and GA4 also lets you set a default value for key events that arrive without one.
- Not retrospective. A key event only counts from the moment you mark it. Past occurrences of the event stay as ordinary events.
- Limits. A standard property allows up to 30 key events, which is far more than most businesses should use.
When you import a key event into Google Ads, it becomes a Google Ads conversion and can feed automated bidding there. That is the distinction Google drew in 2024: key events are GA4’s measure of what matters on your site, while conversions are what Google Ads counts and bids towards.
Why it matters
Key events are the numbers people quote in meetings: how many enquiries the site produced last month, which channel brought the most bookings, what share of sessions led to a sale. If the wrong events are marked, every one of those numbers is wrong, and the reports look perfectly healthy while they are wrong.
The cost is highest when key events feed Google Ads. If a scroll or a newsletter sign-up is imported as a primary conversion, Smart Bidding will happily find you more scrolls and sign-ups, and cost per enquiry will drift up while the account reports success.
UK sites have a further gap to allow for. Visitors who decline analytics cookies on your consent banner are not recorded in the normal way, so the key event count will usually sit below the number of enquiries that actually reached your inbox.
Common mistakes
- Marking engagement signals such as scroll, file_download or video_start as key events alongside genuine enquiries.
- Marking the generic form_submit event from enhanced measurement, which also fires on newsletter boxes and site search forms.
- Basing a key event on a thank-you page that can be refreshed or reached directly, so one enquiry is counted several times.
- Importing a GA4 key event into Google Ads as a primary conversion while the Google Ads tag also counts the same action, which doubles every result.
- Marking a new key event and expecting the previous months to fill in.
How to act on it
Start with a list of the actions that make you money or lead directly to it: an enquiry, a phone call from the site, a booking, a purchase. For most service businesses that is two to five events. Give each one a clear event of its own, using Google’s recommended event names such as generate_lead and purchase where they fit, then mark only those.
Test each one in DebugView by doing the action yourself, set the counting method deliberately and note the date in an annotation so nobody misreads the next month’s report. If key events feed Google Ads, decide which source counts each action for bidding and set the other as secondary. Then check monthly that the key event count roughly tracks the enquiries and orders you actually received.
Choosing and testing key events is part of the tracking set-up I do before any performance marketing campaign, because bidding and reporting both depend on it.