Running out of space on your Mac's internal drive but still want a full, safe backup of your iPhone? You can redirect your iPhone backups straight to an external hard drive — even one that was previously used with a Windows PC. Here's exactly how to do it.

Why bother with this instead of iCloud?

Apple's free iCloud storage runs out fast, and the paid tiers add up to a recurring monthly bill for something you could store once, for free, on a drive you already own. There's a second reason too: an iCloud backup sits on Apple's servers indefinitely — photos, messages, app data, all of it. A local backup on your own external drive means that data never leaves your hands. For anyone backing up business phones, client conversations, or anything you'd rather not have living on a third party's cloud, a local backup is the more private option — and it costs nothing beyond the drive itself.

Why This Isn't as Simple as It Sounds

On Windows, iTunes lets you pick a custom backup location with a couple of clicks. On a Mac, Finder (which now handles iPhone backups since iTunes was retired) doesn't give you that option in the interface at all — it always saves to the same hidden folder on your internal drive.

There's also a second catch: if your external hard drive was previously used on a Windows machine, it's almost certainly formatted as NTFS. Macs can read NTFS drives, but they can't write to them — which means you can't save a backup there until you reformat it.

The good news: both problems have a straightforward fix, and once it's set up, it works automatically every time.

Step 1: Check Your Drive's Format

Plug the external drive into your MacBook.
Open Disk Utility (press Cmd + Space, type "Disk Utility," hit Enter).
Select the drive on the left and check the Format field.

If it says anything other than exFAT or Mac OS Extended, it's likely still in Windows' NTFS format and needs to be reformatted.

Step 2: Reformat the Drive to exFAT

This step erases everything currently on the drive. Back up anything important on it first.

In Disk Utility, select the drive itself (not the volume listed underneath it).
Click Erase.
Set the Format to exFAT — this works on both Mac and Windows, so the drive stays usable on either system.
Set the Scheme to GUID Partition Map.
Click Erase to confirm.

Step 3: Create a Backup Folder on the Drive

Once reformatting is done, open the drive in Finder and create a new folder — for example, iPhoneBackup. Also note the exact name of the drive as shown in Finder's sidebar; you'll need it in the next step.

Step 4: Redirect the Mac's Backup Location (via Terminal)

This is the part that makes the Mac save backups to your external drive automatically, instead of your internal storage.

Open Terminal (Cmd + Space, type "Terminal").

Navigate to the backup folder:

cd ~/Library/Application\ Support/MobileSync

Move the existing backup folder onto your external drive (replace MyDrive with your actual drive name):
```
mv Backup /Volumes/MyDrive/iPhoneBackup
```
Create a shortcut (symlink) so the Mac still finds it in the "normal" spot, but it actually lives on the external drive:
```
ln -s /Volumes/MyDrive/iPhoneBackup Backup
```
Confirm it worked:
```
ls -la
```
You should see a line like Backup -> /Volumes/MyDrive/iPhoneBackup.

Ran into "Operation not permitted" errors? This usually means Terminal needs Full Disk Access. Go to System Settings → Privacy & Security → Full Disk Access, add Terminal to the list, turn its toggle on, then quit and reopen Terminal before trying again.

Step 5: Back Up Your iPhone

Connect your iPhone to the Mac with a cable.
Open Finder and select your iPhone under Locations in the sidebar.
Under the General tab, choose "Back up all of the data on your iPhone to this Mac."
Click Back Up Now.

Leave both devices connected until it finishes — a first backup can take a while depending on how much is on your phone.

Step 6: Verify It Landed on the External Drive

Once the backup completes, open the external drive in Finder and check the iPhoneBackup folder. You should see a new folder named with a long string of letters and numbers — that's your backup. From now on, every backup will go straight to the external drive without you having to repeat any of these steps.

Got stuck on any step, or want to automate this further?

JB Service Solutions helps individuals and businesses set up reliable tech workflows — from device backups to full IT systems.

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How to Back Up Your iPhone to an External Drive on Mac — Even If the Drive Was Used on Windows