If Boot Camp Assistant says that your disk could not be partitioned

Boot Camp Assistant might say that an error occurred while partitioning the disk for Windows.

When attempting to create a Windows partition, Boot Camp Assistant might show the alert ”Your disk could not be partitioned. An error occurred while partitioning the disk. Please run First Aid from within Disk Utility to check and fix the error.”

Use Disk Utility to check for errors

  1. Install the latest macOS updates.

  2. Use Disk Utility to repair your startup disk.

  3. If Disk Utility found no errors or repaired all errors, try again to use Boot Camp Assistant to install Windows.

  4. If Boot Camp Assistant still gives the partitioning error, continue to the steps below.

Check for unallocated free space

  1. Open Disk Utility, which is in the Utilities folder of your Applications folder.

  2. In the Disk Utility sidebar, select the name of your internal disk, container, or volume, such as Macintosh HD.

  3. Click Partition in the toolbar.

  4. If you see a message about Apple File System space sharing, click Partition to confirm that you want to partition instead of add a volume.

  5. If the pie chart shows a section labeled ”Free space,” click to select it. ”Free space” should now also appear in the Partition Information shown on the right.

    macos-mojave-disk-utility-partition

  6. After selecting the ”Free space” section of the chart, click the remove (–) button beneath the chart. Removing this unallocated free space makes that space available for your use again. Then click Apply and quit Disk Utility.

  7. Try again to use Boot Camp Assistant to install Windows.

  8. If Boot Camp Assistant still gives the same partitioning error, continue to the steps below.

Turn off Time Machine temporarily

If you use Time Machine with macOS Mojave or High Sierra, either upgrade to macOS Catalina 10.15 or later, or follow these steps:

  1. Open Time Machine preferences from the Time Machine menuTime Machine menu in the menu bar. Or choose Apple menu  > System Preferences, then click Time Machine.

  2. Deselect ”Back Up Automatically” to turn off Time Machine.

  3. Wait a few minutes, then try again to use Boot Camp Assistant to install Windows.

  4. After installation is complete, you can turn on Time Machine again.

Learn more

Learn what to do if Boot Camp Assistant stops responding or says that Boot Camp installation failed.

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