New and returning overlap

In Google's public GA4 sample of the Merchandise Store, November 2020 has 71,734 new users and 20,207 returning users. So how many users in total? Not 91,941. It's 79,421.

Here's how GA4 counts them:

• New users made their first visit, the first_visit event, in the period.
• Returning users had already started a session before, even a short one.

Someone who visits for the first time on 3 November and comes back on the 10th is both. They're in New users and in Returning users, so adding the two counts them twice.

The longer the period, the more time people have to arrive and come back. In this store, over one day about a quarter of returning users were also new. Over three months, 8 in 10 were.

That share depends on the site. A store with many loyal customers would show much less, but the overlap itself happens everywhere.

"New" means a new browser, not a new person. By default, GA4 recognises website users by a cookie, so the same person on a new phone, or after clearing cookies, is a new user again. Sites that send a User-ID can link those visits.

A few users are neither. About 1% here have no first_visit recorded and no earlier session, so GA4 can't call them new or returning. That's why New users + Returning users − Total users isn't exactly the overlap.

To know how many users you had, use Total users. Never add the other two.

Data: Google's GA4 sample from the Merchandise Store, November 2020 to January 2021, exact counts from BigQuery.