How to Wirelessly Back Up Your Mac to a Windows Computer Using Time Machine

Apple • Ryder Cragie • 22nd June 2022Article Short Link: Short Link:


If you'd like to back up your Mac to an external storage device plugged into another computer on your local network while still being able to use the external storage device to store other files, follow these steps to do so.

Creating a Sparse Bundle Disk Image File in Disk Utility

Save As and Name

Any name that is preferably all one word.


The external storage device.


Choose how much storage on the external storage device you would like to allocate to Time Machine. For instance, if you have a 64 GB external storage device, you may want to keep 12 GB separate from Time Machine, so you would type "50 GB" in this field.


macOS Extended (Journaled).


128-bit AES encryption (recommended). Then you will need to create a password. Do not forget this password.

Image Format

Sparse bundle disk image. This is not to be confused with a "Sparse disk image".


Make sure that the "Size" field hasn't been reset, and then click "Save". Wait for the process to complete.

Allowing the Connection From Your Windows PC to Your Mac

Connecting Your Mac to the External Storage Device Wirelessly

Once your Mac is connected, you will see the external storage device listed under "Locations" in the Finder sidebar, even though it is not physically connected to the Mac. It is now being accessed over your local network. You can place whatever files you want on the external storage device just by dragging it into it.

You will now see the Sparse Bundle Disk Image file listed as a 2nd location in the Finder sidebar. Do not place any files in here — let Time Machine do the work. It is fine to store files outside of this Sparse Bundle Disk Image file on the external storage device though.

Setting Your Mac to Back Up to the Correct Location

sudo tmutil setdestination "/Volumes/TheNameOfYourTimeMachineBackupDrive"

Replace "TheNameOfYourTimeMachineBackupDrive" with the name of the Sparse Bundle Disk Image file you mounted earlier.

If the Time Machine destination has not been changed to the desired location:

Initiating Your First Backup


Done! Your Mac is now backing up over the network!

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