User-ID for cross-platform analysis

Looking for information about where to find your Measurement ID to start collecting data from your website? Go here instead.

User-ID is an advanced feature that 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 see User-ID data starting July 16, 2019.

Reporting identity

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 information from Google signals if that is available. If neither User-ID nor Google-signals information is available, 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).

The option you choose does not affect data collection or processing. You can switch between the options at any time without making any permanent impact on data.

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.

To implement User-ID in your app via the SDK, follow the instructions for iOS or Android.

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.

  1. Sign in to Google Analytics.
  2. Click Admin, and navigate to the property you want to edit.
  3. In the Property column, click Default Reporting Identity.
  4. Select either By User-ID and device (default setting) or By device only.
  5. Click Save.

Report comparisons

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 of data.

Without that comparison applied, you see all signed-in and signed-out data together.

When you include only sign-in users, Analytics deduplicates those users. Because of this, you may notice some differences in your data:

  • 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.

Ads personalization

User IDs that you upload to Google Analytics will be used to process audience lists, which can then be made available to any linked ads services, including for ads personalization. Currently, we only support the targeting of the last device seen for any given user ID. You may configure criteria that require usage across multiple devices/platforms (e.g., an audience that requires a purchase event from both web and app streams). You may also configure device-specific or stream-specific criteria to maintain device-centric audiences.

Limits and guidelines

Learn more about the limits to User-ID and the guidelines you need to observe.

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