Setting user IDs accurately is important for Google Analytics data and reporting accuracy. The User-ID feature lets you associate your own identifiers with individual users so you can connect their behavior across different sessions and on various devices and platforms. Analytics interprets each user ID as a separate user, which provides you with more accurate user counts and a more holistic story about a user's relationship with your business.
To send user IDs to Analytics, you need to create a unique ID for each user on your own and assign and consistently reassign the IDs to your users. This is typically done during login. For example, when a user signs in, you could use their email address to generate a unique ID that you can reference throughout your website or application. Each user ID must be 256 characters or less.
When the User-ID value is set incorrectly, there can be significant impact to your Google Analytics property, including misattribution across reports, and a permanent impact to historical data. Learn more about User-ID.
Diagnostics for User-ID implementations
- Global banner: if your User-ID implementation is causing limits to be reached, a diagnostic will appear in the global banner. Your data will be impacted. Learn more about limits and how to resolve the issue.
- Reports: if your User-ID implementation is impacting data specific to reports in Google Analytics, a diagnostic will appear in the Data quality indicator.