The User-ID feature lets Analytics present a cross-platform, cross-device view of your users' behavior.
To use this feature, you have to be able to generate your own unique, persistent IDs, consistently assign those IDs to your users, and include the IDs along with the data you send to Analytics.
Analytics creates a single user journey from all the data that is associated with the same user ID.
You can choose one of two methods to identify user data for reporting:
- By User-ID and device: this method uses the more accurate User-ID if it is collected to identify a user and unify all related events in reporting and analysis. If no User-ID is collected, then Analytics uses a device ID, either the Analytics cookie for websites or the App-Instance ID for apps, to identify a user.
- By device: this method uses only the device ID, either the Analytics cookie for websites or the App-Instance ID for apps, to identify a user, and ignores any User-IDs that were collected.
You can find these options in Analytics Admin under Default Reporting Identity (see below).
Changes in user metrics
When you implement User-ID, Analytics begins processing user IDs (when Analytics collects them) for each event, making your reports more accurately reflect your users' logged-in behavior across platforms and devices. As a result, you should expect user metrics to change from the point of implementation onward. The nature of the change depends on how users interact with your business. For example, the Active Users metrics, which count active users over periods of days (e.g., 7, 14, 28), are likely to experience fluctuations immediately following implementation as individual users may be counted as both logged in and logged out during those times. This is expected, and your data will assume a new normal after the associated period (e.g., 7, 14, 28) has passed.
You implement User-ID first in your site or app, and then in Analytics Admin.
In your site or app
To implement User-ID on your website via the global site tag, follow these instructions.
In Analytics Admin
After you update your site or app to collect user IDs, you can update your property configuration in Analytics Admin to change the reporting identity you want to use.
- Sign in to Google Analytics.
- Click Admin, and navigate to the property you want to edit.
- In the Property column, click Default Reporting Identity.
- Select either By User-ID and device (default setting) or By device only.
- Click Save.
After you implement User-ID in your site/app and confirm the settings of your Analytics property, you can add comparisons to your reports to compare signed-in data to other types.
Without that comparison applied, you see all signed-in and signed-out data together.
When you include only signed-in users, you may notice some differences in your data since Analytics is deduplicating those users:
- Lower user counts
- Higher per-user values
You'll also see additional data like how many of those users engaged with your business on multiple platforms.
Limits and guidelines
Learn more about the limits to User-ID and the guidelines you need to observe.