Time Machine not backing up after migrating to a new Mac with less storage capacity

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Time Machine not backing up after migrating to a new Mac with less storage capacity

I have recently upgraded my Mac from a late 2014 iMac to a new M4 model. Both machines were sold as having 1TB storage (Fusion Drive on the old one, SSD on the new).

First problem: I couldn't migrate information from the backup drive because I found that the old HDD had effectively more space than the new SSD (1.12TB Vs 1TB), so I purchased another external disc and offloaded about 500GB. I deleted the files from the old Mac and backed it up. The remaining data and applications migrated over to the new Mac, but now Time Machine won't back up.

[Re-Titled by Moderator]

Original Title: Delayed backup

iMac 24″, macOS 26.2

Posted on Dec 21, 2025 2:39 PM

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Answer 1

Dec 21, 2025 3:09 PM in response to philiplewin

Starting backups on a New Mac has some complexity. To understand where you are in the process, Readers need more than:

<< Time Machine won't back up. >>

What have you done to encourage Time machine to back up?

How did you decide it worn't ?

EXACTLY what error messages did you get?

what is the current state of the Time Machine settings pane?

this article discusses some of the issues:

If your new Mac inherits your backup history - Apple Support

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