A key event is an event in Google Analytics 4 (GA4) that a property owner has flagged as especially important to the business - a purchase, a lead form submission, an app install. Google defines it as "an event that measures an action that's particularly important to the success of your business." The label exists because of a naming problem. Until March 2024, GA4 called these actions conversions, while Google Ads used the same word for something narrower: actions used to measure campaigns and steer automated bidding. The two counts rarely matched, so Google gave the analytics version a new name.

How an event becomes a key event

GA4 records everything as events, from page views to purchases, and none is special until someone marks it. In the interface, an editor goes to Admin, then Data display, then Events, and clicks the star next to an event name. A new event can also be created with the "Mark as key event" switch turned on, at which point a default value and a counting method are chosen.

Some events are starred automatically. According to Google's help centre, purchase is a default key event on web and app, while first_open, in_app_purchase, app_store_subscription_convert and app_store_subscription_renew are defaults for apps only. When ads personalisation is on and a Google Ads account is linked, seven more can be marked, including add_to_cart, begin_checkout and view_item. Since June 12, 2025, properties that choose lead generation as their business objective have had the qualified and converted lead events set as key events automatically, a default that can be switched off.

Limits are fixed. A standard property can mark up to 30 events as key events; an Analytics 360 property can mark 50, according to Google. Marking is not retroactive. Reports start counting from the moment the star is set, standard reports can take up to 24 hours to show the change, and unstarring an event leaves historical counts intact.

The events themselves arrive through the Google site tag, Google Tag Manager, the Firebase SDK for apps or the Measurement Protocol. Google publishes recommended event names with prescribed parameters, such as generate_lead or purchase with value, currency and items, but any custom event can be starred.

Counting and attribution

Each key event has one of two counting methods. "Once per event", which Google labels recommended, counts every occurrence. "Once per session", which Google labels legacy, counts at most one per session. If a visitor submits a form five times in one visit, the first method records five key events and the second records one. Once per session is the default only for key events created from Universal Analytics goals, either in automatically created properties or through the goals migration tool used after April 2023. Everything else defaults to once per event.

Credit is then assigned to traffic sources by an attribution model set at property level. GA4 offers data-driven attribution, paid and organic last click, and Google paid channels last click. The last of those can hand 100% of the credit to the final Google Ads click, a choice Chris Long criticised publicly in May 2024. The default lookback window for key events is 90 days, adjustable to 60 or 30, as PPC Land noted when 59% of 624 poll respondents misread how GA4 assigns session source in December 2025.

Two rate metrics sit on top. User key event rate and session key event rate, added to the acquisition reports in June 2024, measure the share of users or sessions with at least one key event. A site with 20,000 sessions, 600 of which include a purchase or sign-up, shows a session key event rate of 3%, regardless of how many key events those 600 sessions contain.

From key event to Google Ads conversion

A key event is not automatically a Google Ads conversion. To bid on it, an advertiser creates a conversion from it, which requires a linked Google Ads account. Google allows one web and one app conversion per key event in each linked account, and any GA4 event chosen for this purpose is starred as a key event if it was not already. Inside Google Ads, the resulting conversion action is set as primary, counted in the Conversions column and used for bidding, or secondary, counted only in All conversions.

Google Ads conversions appear in GA4's Advertising section, in the Conversion performance report and the Conversion management page, not in standard reports. Shared conversions carry no historical data, and Google says it has no plan to export Google Ads conversions to BigQuery. The raw events behind key events still flow to the BigQuery export, capped at 1 million events a day for standard properties in the daily batch.

Origin and evolution

The ancestor is the goal in Universal Analytics (UA). Goals were configured per reporting view, capped at 20 per view in sets of five, and came in four types: destination, duration, pages or screens per session, and event. A completed goal was recorded as a conversion, at most once per session.

Google introduced App + Web properties in beta in 2019 and relaunched them as Google Analytics 4 on October 14, 2020, announced by Vidhya Srinivasan of Google Ads. The event model replaced goals with a simpler mechanism: star an event and it became a conversion. On March 16, 2022, Russell Ketchum, a Google Analytics product director, announced that standard UA properties would stop processing data on July 1, 2023, with UA 360 following on July 1, 2024. PPC Land tracked the 360 shutdown schedule, including the deprecation of UA conversion export and bidding on January 29, 2024.

The once per session option arrived in April 2023, according to Search Engine Journal, to ease comparisons with UA. The rename followed in March 2024. PPC Land reported on March 21 that GA4 and Google Ads would share conversion definitions, with key events replacing GA4 conversions. "Now, conversions in the existing report and explore modules will become key events," Kamal Janardhan, senior director of product management for measurement at Google, said, according to Search Engine Land. Google told advertisers no action was required and moved advertiser reports into the Advertising section. In February 2025, Merchant Center adopted the same language, renaming "conversion tracking setup" to "key event setup".

Why it matters

For marketers, key events are the yardstick that most GA4 reporting is built around. They decide which actions appear as outcomes in acquisition reports, which actions can become bidding signals, and which numbers flow into downstream metrics such as average order value or return calculations. A wrong star inflates or deflates every rate that depends on it. A duplicate purchase tag, for instance, doubles key events silently unless a transaction ID is in place, as PPC Land's deduplication explainer describes.

The rename also settled a recurring dispute. Analysts had compared "conversions" in GA4 and Google Ads and found different totals, produced by different models, windows and counting rules. Since 2024 the words point to different objects.

Limitations and criticisms

Naming confusion did not end with the rename. Older documentation and dashboards use the pre-2024 label, and GA4 itself now reports both key events and conversions in separate places with separate settings.

Data gaps affect counts. When users decline analytics cookies, Google can model their behaviour through behavioural modelling for consent mode, but only for properties with at least 1,000 daily events from non-consenting users over seven days and 1,000 daily consenting users on seven of the previous 28 days. Smaller sites get no modelling. Misconfigured consent mode can remove data altogether: one advertiser's Google Ads conversions fell 90% overnight in August 2025 because consent signals were not passed to tags.

Thresholds and retention limit analysis. GA4 withholds rows when demographic data or small user counts could identify individuals, and the thresholds cannot be adjusted. Retention of event-level data in explorations is 2 or 14 months on standard properties, and up to 50 months on 360, according to Google. Standard aggregated reports are not affected.

Attribution choice remains contested, particularly the Google paid channels model, which favours Google's own ad inventory by design.

Not the same as

Event is any interaction GA4 records. A key event is an event someone has marked as important.

Conversion, in Google's current vocabulary, is a Google Ads object created from a key event or other source and used for campaign measurement and bidding.

Goal was the UA mechanism, defined per view by destination, duration, pages per session or event. Goals ended with UA.

Google Ads conversion action is the configured item inside Google Ads, with its own window, counting and primary or secondary status. A GA4 key event can feed one, but the two are counted separately.

Outside Google, other tools use other terms. Adobe Analytics calls comparable actions success events, with up to 1,000 available, according to Adobe's documentation. The phrase "key event" in general usage simply means an important occurrence.

Recent developments

On January 16, 2026, Google began testing conversion management with per-conversion attribution settings, stating that key event settings remain independent of conversion settings except for default values. Cross-channel conversion data reached the Data API in alpha on May 4, 2026, covering conversions but not key events. On August 11, 2026, Google made conversion windows editable to any whole number of days, 1 to 90 for clicks and 1 to 30 for engaged views. As of October 2026, Google's Site Kit plugin for WordPress reports key action rates that resemble GA4's session key event rate, built from events sent by eight form and commerce plugins.

Timeline

  • 2019: Google introduces App + Web properties in beta, combining app and web data on an event model.
  • October 14, 2020: Google launches Google Analytics 4, in which marked events are called conversions.
  • March 16, 2022: Google announces that standard Universal Analytics properties will stop processing data on July 1, 2023, and 360 properties on July 1, 2024.
  • April 2023: GA4 adds a once per session counting option alongside once per event.
  • July 1, 2023: Standard Universal Analytics properties stop processing new hits.
  • March 2024: Google renames GA4 conversions to key events and aligns the term conversion with Google Ads.
  • June 2024: GA4 adds user key event rate and session key event rate to acquisition reports.
  • July 1, 2024: Universal Analytics 360 properties stop processing data and access ends.
  • February 2025: Merchant Center renames conversion tracking setup to key event setup.
  • June 12, 2025: GA4 begins auto-configuring key events for lead generation properties.
  • January 16, 2026: Google tests conversion management and per-conversion attribution settings in GA4.
  • May 4, 2026: Cross-channel conversion reporting reaches the GA4 Data API in alpha.
  • August 11, 2026: Conversion windows become editable to any whole number of days.

Summary

  • Who: Google defines and operates key events in Google Analytics 4; site owners, analysts and marketers mark them; advertisers turn them into Google Ads conversions for bidding.
  • What: An event in GA4 flagged as particularly important to a business, counted once per event or once per session and attributed to traffic sources through a property-level model.
  • When: GA4 launched with "conversions" on October 14, 2020; Google renamed them key events in March 2024, and has since separated conversion settings, reports and APIs through 2026.
  • Where: In GA4 reports and explorations, the Admin events settings, the Advertising section when shared with Google Ads, Merchant Center, and the BigQuery export of raw events.
  • Why: To give businesses a way to measure the actions that matter in analytics, while keeping that count separate from the conversions Google Ads uses to measure campaigns and set bids.