Reporting identity is the GA4 setting that decides how Google Analytics recognises the same person across visits and devices when it counts users in your reports. You choose between Blended, Observed and Device-based, and the choice changes user counts and some attribution without changing the raw data GA4 collected.
How reporting identity works
GA4 can draw on several kinds of identifier, in order of preference:
- User ID: your own identifier for a signed-in customer, sent by your site or app when someone logs in.
- Device ID: the random identifier stored in the _ga cookie on a website, or the app instance ID in an app.
- Modelling: modelled data that estimates the activity of visitors who declined analytics cookies, based on similar visitors who accepted. It needs consent mode running in advanced mode and a property that meets Google’s eligibility requirements.
Blended uses all three, starting with User ID, then device ID, then modelling to fill the gaps. Observed uses User ID and device ID but no modelling. Device-based uses only the device ID and ignores User ID. The setting is in GA4 Admin under data display. Google has changed what each option includes over the years, and at the time of writing (October 2026) Google signals no longer feeds into reporting identity, so check Google’s help pages for the current definitions.
The setting is not destructive. Switching options recalculates reports, including past periods, rather than altering stored data, so you can compare the options and switch back.
Why it matters
The same site can show noticeably different user counts under each option. On a UK site where many visitors decline cookies, Blended usually shows fuller user and conversion figures, because modelling estimates part of the missing activity. Device-based tends to overcount people, because one customer on a phone and a laptop appears as two users.
Consistency matters as much as the choice. If the identity changes partway through a year, figures exported or screenshotted under the old setting will no longer match what GA4 shows for the same period. And modelled figures are estimates: useful for trends, but never something to present as counted visitors, especially when your own order or enquiry records are available.
Common mistakes
- Not knowing which option the property uses, then comparing figures with a colleague’s export made under a different one.
- Choosing Blended and presenting modelled users to a board or investor as if they were counted people.
- Sending an email address or other personal information as the User ID. Google’s policies forbid sending personally identifiable information to GA4, and it raises UK GDPR questions about what you are sharing.
- Expecting Blended to add modelled data when consent mode runs in basic mode or the property is not eligible.
- Changing the setting to make one month’s results look better.
How to act on it
Check the current setting in Admin and record it in the definitions on your report template. If your site has customer logins, send a non-personal User ID, such as an internal customer number, at sign-in so journeys across devices join up. If you use advanced consent mode, check on the reporting identity page whether the property is eligible for modelling.
Pick one option for routine reporting and keep it. Blended is a sensible default where modelling is available, with Observed as a cross-check on counted data. I review this setting alongside the consent and tag setup in performance marketing, because user and conversion figures are only comparable when everyone knows which identity produced them.