Time Machine Backup Size Issue: Size ballooned for no reason

A 124 GB incremental backup usually means Time Machine sees a large amount of data as changed, even if you didn’t intentionally add 124 GB of files.

One possibility is a large file or database that was rewritten by an app. Apple specifically notes that some apps keep data in large files, and Time Machine will back the whole changed file again.

I wouldn’t delete snapshots just to avoid this backup. Local Time Machine snapshots are managed automatically and are removed as they age or when space is needed.

If the backup completes normally, I’d probably let it finish and see whether the next hourly backup returns to its usual size. If the next few are also unusually large, then it would be worth looking for a large, frequently modified file or app data that’s triggering it.

If Time Machine takes a long time to back up - Apple Support offers a few reasons, not all of which address the unusually large incremental backup size as such, but it's worth reviewing.

Needless to say, if you are using any non-Apple "anti-virus", "cleaning", or "Internet security" products including "banking security", anything at all in that broad category of utterly useless garbage, don't. A lot of things won't work if you do. The above Support document makes mention of it but it's easily overlooked.

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