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User ID

A user ID is a unique identifier you assign to a logged-in user so analytics can recognise them across devices and sessions.

Written by Reflective Data experts · updated Oct 5, 2026

With a user ID, activity from a phone, a laptop and a tablet can be stitched into one user journey. It improves counts of unique users and enables better retention and lifetime analysis.

Never use an email address or other directly identifying value as the ID. Use an internal, hashed or random identifier.

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Cohort analysisNew vs returning usersUser property

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