Hi Christina,

Thank you for contacting Amplitude Support. I'd be happy to help!

Amplitude uses a system of User IDs, Device IDs, and Amplitude IDs to track unique users. A user can have multiple Device IDs and Amplitude IDs, but each unique user can only have one User ID. If a user performs events on multiple devices but logs into their account, they are still counted as one unique user.

Currently, Amplitude does not support calculating retention by Device ID alone. Instead, we use a combination of User IDs, Device IDs, and Amplitude IDs to track unique users and calculate retention. You can read more about how we track unique users here: https://amplitude.com/docs/data/sources/instrument-track-unique-users

Could you please share more about your specific use case and why calculating retention by Device ID is important for your analysis? Understanding your goals will allow us to better assist you with potential workarounds or alternative approaches that might meet your needs within Amplitude's current capabilities.

Looking forward to your response!

Best regards,
Thao


P.S. Checkout upcoming events and user meetups on our events page.

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