Can you reformat an external drive to a Mac without losing data?

Reformatting an external hard drive from Windows to Mac can be a tricky process if you want to preserve the data already on the drive. When Windows formats a drive, it uses the NTFS file system, while Macs rely on HFS+. This means that while a Mac can read files on an NTFS drive, it cannot write to it. So reformatting the drive will make it fully compatible with Mac, but could potentially erase all the data. Luckily, it is possible to reformat the drive without losing data through some careful file migration. This article will walk through the step-by-step process.

Back Up Your Data

Before attempting to reformat your external drive for Mac, it is critically important that you back up all of the data on the drive first. Reformatting will erase everything currently on the drive, so you want to make sure none of that data is lost in the process.

The best practice is to back up the entire external drive to another external drive or storage location using a backup service like Time Machine on Mac. Time Machine makes it easy to do a full backup of your external drive to another external hard drive or network location (source).

You can also manually copy all of the files on the external drive over to another drive or cloud storage. The key is making sure you have a second copy of that data before proceeding with any reformatting.

Backing up the external drive ahead of time ensures you have a copy of all your data and files in case anything goes wrong during the reformatting process. Don’t skip this crucial first step!

Check the Drive’s Format

The first step is to check the format of your external hard drive. This will tell you if the drive is already formatted for Mac or still retains the Windows format.

To check the format on Mac:

  1. Connect the external hard drive to your Mac.
  2. Open Finder and locate the drive in the left sidebar under Devices.
  3. Right click on the drive and select “Get Info.”
  4. In the info window that opens, look at the “Format” section.
  5. If it says “NTFS” or “FAT32”, then the drive is still formatted for Windows.
  6. If it says “Mac OS Extended (Journaled)” or “APFS”, then the drive has already been formatted for Mac.

Knowing the current format will determine the next steps to take in the process.

For example, if the drive shows “NTFS”, you cannot directly write to it on Mac OS. So you would need to reformat it before migrating data.

Checking the format is crucial to understand if reformatting is necessary and what potential data migration is required.

Use a Third-Party NTFS App

If you don’t want to reformat the external drive, another option is to use a third-party NTFS app that enables MacOS to read and write to NTFS drives. Popular choices include Paragon NTFS ( and Tuxera NTFS (

These apps install a driver that adds NTFS support to MacOS, allowing full read/write capability. Once installed, you can simply plug in your NTFS external drive and access the files just like any other drive. The apps typically offer a 10-14 day free trial to test them out.

The benefit of this approach is you can use your external drive for both Windows and Mac without reformatting. The downside is you need to purchase the app to enable NTFS support long-term. But for many users who go back and forth between Mac and Windows, a third-party NTFS app is an ideal solution.

Reformat the Drive

To reformat an external drive on a Mac without losing data, you’ll want to use the Disk Utility app that comes pre-installed on all Macs. Here is a step-by-step guide for using Disk Utility to reformat a drive:

  1. Connect the external drive you want to reformat to your Mac.
  2. Open Disk Utility (located in Applications > Utilities).
  3. In the sidebar, select the external drive you want to reformat.
  4. Click the “Erase” tab.
  5. Give your drive a name and select “Mac OS Extended (Journaled)” as the format.
  6. Click “Erase” to start reformatting the drive.

This will quickly reformat the drive without deleting any data. According to Apple’s support article (Erase and reformat a storage device in Disk Utility on Mac), this is possible because Disk Utility only erases the drive’s directory structure and not the data itself. The data remains intact until new files overwrite it. So reformatting does not delete your data as long as you do not save new files to the reformatted drive.

Potential Issues

When reformatting an external drive, there is a risk of data corruption or loss. Some potential issues to be aware of include:

  • If the reformatting process is interrupted, it may corrupt data on the drive and make files unreadable. This can happen if the computer shuts down unexpectedly during reformatting.
  • Any files already on the external drive will be erased during a reformat. Be absolutely certain you have backups of anything important before reformatting.
  • If there are bad sectors on the external drive, reformatting may make that portion of the disk unusable. Any data stored in bad sectors could be lost.
  • Drives formatted for Windows using NTFS may develop corruption over time when used on Mac. Reformatting cleans away any underlying corruption.
  • Fragmented data on a drive slated for reformatting may not migrate properly to the new format. Defragmenting beforehand avoids this issue.

To avoid potential data loss, thoroughly back up the external drive before attempting reformatting. Also scan for and repair any disk errors beforehand. Monitor the reformatting process closely in case manual interruption is required.

Migrate the Data

Once the external drive is reformatted for Mac, you’ll need to transfer your files and data over from the old external drive. Here are the steps for migrating the data:

1. Connect both the old and new external drives to your Mac using USB cables. Make sure both drives mount successfully.

2. Open Finder and locate the old external drive. Select the files and folders you want to transfer to the new drive.

3. Drag and drop the selected files/folders from the old drive to the new external drive location.

4. If you want to migrate the entire contents of the old drive, you can use Apple’s Migration Assistant application. Open Migration Assistant and select the option “From a Mac, PC, Time Machine backup, or other disk”. Then select the old external drive as the source and the new drive as the destination.

5. Migration Assistant will transfer all user accounts, applications, settings, and files from the old drive to the new one. This makes sure nothing gets left behind.

6. Once the migration is complete, verify the files and data were transferred properly by spot checking folders on the new drive. You can then erase and reformat the old drive if no longer needed.

Verify Successful Migration

Once the migration process is complete, it’s important to verify that all your data was successfully transferred to the external drive. Here are some steps you can follow to confirm everything migrated correctly:

1. Open the Finder window and navigate to the external drive. Browse through the folders and make sure all your files and folders are present.

2. Open applications like Photos, iTunes, Documents and browse through your libraries. Verify your photos, music, documents are accessible from the external drive. As per discussions on Apple forums, you can open the iPhoto library directly from your external drive to check images (

3. Check that large files like movies transferred correctly by sampling some to see if they open and play properly from the external drive.

4. Use Finder’s Sort By options like Date Modified and Date Created to spot check files created/modified on certain dates to confirm they migrated.

5. As a final verification, you can use a third party data migration checking tool. Some options are EaseUS Todo Migration Software and Prosoft Data Rescue. These can scan the drives and validate successful data migration.

Using the Drive on Both OS

If you want to use your external drive on both Windows and Mac computers without losing data, the best solution is to format the drive to ExFAT.

ExFAT is a file system that is compatible with both Windows and macOS. When you format to ExFAT, you’ll be able to read and write files to the drive from either operating system without any special software.1

To format to ExFAT, first back up any important data from the drive. Then in Disk Utility on your Mac, select the drive and click Erase. Choose ExFAT as the format and click Erase to reformat the drive.

Once formatted to ExFAT, you can freely use the external drive between your Mac and Windows computers without worrying about losing data. The drive contents will be fully accessible from either OS.

One thing to note is that you may lose the ability to use some Mac-specific features like Time Machine backups on ExFAT drives. But you gain the ability to seamlessly share external storage between Mac and Windows.


In summary, there are a few main steps to reformat an external drive from Windows to Mac without losing data:

– First, backup any important data on the external drive to another location.

– Check the external drive’s current format. It is likely formatted in NTFS for Windows.

– Use a third party NTFS app to read/write files on the NTFS drive on your Mac.

– Use Disk Utility to reformat the external drive to a Mac compatible format like APFS or exFAT.

– Migrate the data back to the newly formatted external drive.

– Verify the data migration was successful and you can access all files.

– If you want to use the external drive on both Windows and Mac going forward, exFAT is likely the best format.

Following this process will allow you to reformat an external drive from Windows to Mac without losing any data in the migration.