should back up take over 12 hours
My time machines is taking over 12 hours to back up and still has a long way to go. Is this normal?
MacBook Pro with Retina display, Time machine
How much data (in GB) are you backing up?
What type of connection (Thunderbolt, USB 3.0, USB 2.0, etc.) do you have to your external drive?
Is this the initial Time Machine backup, or is this just an incremental one (you've done full backups before, and this is just backing up one or two changed files).