Why isn't Time Machine backing up automatically?

byomtov wrote:

Time Machine is not running automatically, even though I do have the "Back up Automatically" box checked.

When I open System Preferences it gives a time for the next backup, but then doesn't execute it. It does work when I hit "Back up now."

This has been going on for some time, and I have definitely changed some files in that period.

To minimize the risk of needing to create a new backup, consider doing the following:

• Ensure that your external backup disk’s firmware is up to date. If you back up to a Time Capsule, check the Apple Support website to be sure you have the most current firmware available.

• Use Server Message Block (SMB) to back up to your external backup disk.

• Use an uninterrupted power supply (UPS) with your external backup disk to prevent unexpected power failures.

• Disable write caching on your network storage device, if it allows it.

reference:

If you need to create a new backup from Mac—

https://support.apple.com/guide/mac-help/if-you-need-to-create-a-new-backup-mh34042/11.0/mac/11.0

I found this older discussion with apparently a solution: https://discussions.apple.com/thread/7885020

Those times are estimated. If you are actively using the computer the backup may not happen. Leave it alone and see if backups are happening when you aren't looking.

Have you installed any 3rd party software to change how Time Machine works?

Are you absolutely sure Time Machine is not running? You can check the Time Machine backup timestamps by running "tmutil listbackups" in the Terminal app (be patient, this takes a while)

Excellent! Thanks for letting the community know.