iPhone backups are taking up space on your Mac. Where they are, and which ones you can delete

Plug an iPhone into a Mac, click Back Up Now once, and the Mac keeps a full copy of that phone forever. Not a diff. The whole thing, photos included if they were on the device. Do it for two phones and an iPad over a few years and it is 100 GB in a folder nothing ever shows you.

Where they are

~/Library/Application Support/MobileSync/Backup/

One folder per device, named by the device's hardware identifier, so the folder names mean nothing. Sizes are easy though:

du -sh ~/Library/Application\ Support/MobileSync/Backup/* 2>/dev/null | sort -rh

To match a folder to a device, open Finder, select the iPhone in the sidebar (or any iPhone; the list is the same), and click Manage Backups. That window lists every backup with the device name, the date, and a Delete button. It is the right place to delete from, because it also clears the record Finder keeps of the backup.

Which ones to delete

A device you still use, backing up to this Mac. Keep the latest backup. Older ones for the same device are superseded, unless you are keeping one from before a specific event on purpose.

A device you still use, backing up to iCloud. The Mac backup is a stale copy from whenever you last plugged in. Safe to delete; iCloud has a newer one.

A device you replaced and restored from. The restore moved the data to the new phone, which has its own backups. Safe to delete.

A device you no longer have and never restored. This backup is the only copy of whatever was on it. Delete it only once you have decided you do not want that data, or after copying the folder somewhere else.

That last case is why iPhone backups are the one thing on a Mac cleaner's list that should never be labelled safe.

Encrypted backups

A backup made with Encrypt local backup on carries Health data, saved passwords and Wi-Fi settings, and is the only kind that can restore them. If you are keeping one backup per device, keep the encrypted one.

Stopping them from growing back

In the same Finder pane, the Back up your most important data option switches the device to iCloud. Or leave it on the Mac and delete the previous backup each time a new one completes; the Mac keeps only one backup per device unless you archived one.

Where Decruft fits

Decruft lists each backup folder with its size and date and moves the ones you pick to the Trash. It labels every backup review-first, never safe, and says why. The Manage Backups window in Finder is the better tool when you need device names; Decruft is the one that shows the backups next to everything else eating the disk.