Guide 169 · Conversions · GA4 + Tag Manager
The default key events GA4 creates: purchase, and what is already marked for you
A new property is not empty of key events. GA4 marks the purchase event as a key event on its own, so an ecommerce site has its main outcome marked before anyone opens Admin. This guide lists what GA4 marks for you, shows how to check the list, and works out how many of the 30 slots a new shop has already used.
After the steps, the purchase key event appears under the Key events tab in Admin, and the standard reports show it within a day. The worked example below gives the count and the rate to expect.
Download the reference: the purchase key-event reference (JSON) (795 bytes, MD5 8a46acfa7f3ea006033fcfc215a25ad4). It holds the event name, the counting method, the worked-example figures recomputed for this guide, and the checkpoints that prove the key event is recording. The figures in the file are the same figures shown on this page.
What you need
- Editor access or above at property level in GA4. Marking an event as a key event is a property setting, and the star in the Events table does not appear for a Viewer.
- A property with ecommerce data, or at least a purchase event collected once, so the default marking is visible in the Key events tab.
- The knowledge that the limit is 30 key events for a standard property and 50 for Analytics 360. Defaults count against that limit in the same way as events you mark yourself.
The trace
- Open Admin, then Data display, then Events, then the Key events tab. Before you mark anything, read this list. On a property that has collected a purchase, the purchase row is already there, marked by GA4 itself.
- Confirm purchase is the event doing the work. Google's help pages state that GA4 automatically flags the purchase event as a key event, because purchase is the event that tells GA4 an ecommerce transaction has happened. No star click is needed for it.
- Count what is already marked. In the worked example the property shows purchase and nothing else, so 1 of the 30 slots is used and 29 stay open. A property that also collects app events can show more defaults; count the rows, do not guess.
- Do not mark purchase a second time. There is no second marking to apply. Clicking the star on an already-marked event removes the marking, which is the opposite of what an ecommerce site wants.
- Mark the step before the purchase, if you need it in reports. begin_checkout is not a default key event. If the business wants to see checkouts that never became purchases, mark begin_checkout as well, and the count becomes 2 of 30.
- Check the share of sessions that bought. In the worked example, 96 of 2,000 sessions included a purchase, which is a session key event rate for purchase of 4.80%. That single rate is the number the shop reports, not the raw count of purchases.
Dead ends
DEAD END — MARKING purchase BECAUSE THE TAB LOOKS EMPTY. If the Key events tab is empty on a property that has never collected a purchase, the fix is to collect a purchase, not to mark a different event and call it the purchase. The default appears when the event arrives.
DEAD END — COUNTING SLOTS FROM MEMORY. Defaults and migrated goals both occupy slots. A property migrated from Universal Analytics can arrive with goals converted to key events already filling the list. Read the tab; the count on the page is the count that matters.
DEAD END — ASSUMING EVERY RECOMMENDED EVENT IS A DEFAULT. add_to_cart, begin_checkout, and view_item are recommended events, not default key events. Only purchase is marked for you on the web side. Mark the rest deliberately, or they never appear in key event reports.
End state
The purchase event is marked by GA4 itself, and the property holds 1 marked event of 30. The worked example below is a 28-day window for a small shop with 2,000 sessions and 1,500 users.
| Figure | Value |
|---|---|
| Sessions in the window | 2,000 |
| Users in the window | 1,500 |
| Purchase events collected | 104 |
| Sessions with a purchase | 96 |
| Session key event rate for purchase | 4.80% |
| Users who purchased | 88 |
| User key event rate for purchase | 5.87% |
| Key events marked, of 30 allowed | 1 of 30 |
The session rate is 96 / 2,000 = 4.80% and the user rate is 88 / 1,500 = 5.87%, both recomputed in Python 3 and rounded to two places. The 104 purchase events came from 96 sessions, so 8 sessions bought twice. The figures are a worked example, not a real property.
Sources
- Analytics Help — About key events — marking an event as a key event, the 30-event limit for a standard property, and 50 for Analytics 360
- Analytics Help — Conversions vs. key events in Google Analytics — what a key event is, the event to key event to conversion flow, and where Google Ads conversions appear
- Google Analytics developer docs — Measure ecommerce — the purchase event parameters, and value as the sum of price times quantity without tax or shipping
Checked 11 November 2026. The click path above is the one in Google's help pages, read 11 November 2026. GA4 automatically flagging purchase as a key event, and the limits of 30 for a standard property and 50 for Analytics 360, are as Google documents them. No step in this guide was run inside a live Analytics property, because Admin needs a Google sign-in and this site does not sign in as anyone. The figures on this page are a worked example recomputed in Python 3 with decimal arithmetic, not numbers from a real property. Google moves menu items without warning; if a path on this page no longer matches, the linked help page is the current map.