How to revert to macOS Catalina from Big Sur

No matter how great macOS Big Sur is, you can experience performance issues as you update your Mac. The good thing is you can downgrade to the previous macOS version. The process is a bit lengthy and complicated, but we’ll provide step-by-step instructions. So, here’s how to downgrade from macOS Big Sur to Catalina.

First, back up everything

Your Mac probably contains your personal data and documents that you don’t want to lose. So, to keep those alive after the downgrade, you need to back up your data.

You can use Google Drive, iCloud Drive, or any other cloud you prefer – just make sure you back up everything.

Before you copy all your documents, photos, and videos to the drive, it’s better to organize every piece of data to avoid clutter. Transferring your information, you may simultaneously copy junk and old logs to your drive too. To prevent this, use CleanMyMac X.

CleanMyMac X is a dedicated Mac cleaner that helps to deal with all types of junk: outdated cache, old log files, temporary files, and more! Here’s how to clear up your storage space before you back up all your data:

  1. Download CleanMyMac X (a free trial is available).
  2. Install and launch the app.
  3. Press Scan.
  4. When CleanMyMac X finished scanning, press Run to remove all junk or
  5. Click Review to manually select what you want to remove.

Now, all junk and clutter are gone, and you can back up everything!


Open this article on your phone to make sure you do everything step-by-step.

How to downgrade from macOS Big Sur

If you’ve updated your macOS to Big Sur, but things didn't go as expected, here’s how to downgrade.

1. Erase your Mac’s hard drive

    The first step is plugging your Mac into power (the downgrading may take a while, and you don’t want your Mac to power off unexpectedly).

    You’ll need to erase your Mac’s drive. This will remove everything from your Mac, but you can restore your data later from a Time Machine backup.

    1. Restart your Mac (Apple menu > Restart).
    2. Hold Command-R when your Mac’s rebooting. The Utilities menu should appear.
    3. Choose Disk Utility.
    4. Click Continue and select Startup Disk (usually located at the top of the list ).
    5. Press Erase.
    6. Select the APFS file format.
    7. Choose GUID Partition Map and confirm.

    Wait for the process to complete. Only after every piece of data is removed, can you clean install macOS Catalina.

    2. Use Time Machine to restore your backup

    You can now restore all your files and data and bring your Mac back to the condition it was in before you installed macOS Big Sur.


    If your Time Machine backup is stored on the external drive, plug it in your Mac.

    So, to restore your Time Machine Catalina backup:

    • Restart your computer and hold Command-R when it reboots.
    • Select the Restore From Time Machine Backup option on the Utilities window.
    • Press Continue.
    • Choose your Time Machine backup disk.
    • Select the backup you want to restore from. Choose the most recent backup that occurred before you installed macOS Big Sur.
    • Then, select a destination disk, where the contents of your backup will be stored.
    • Click Restore and press Continue.

    The process may take some time. Your Mac will restart running macOS Catalina.

    Roll back to macOS Catalina using a bootable installer

    If you didn’t back up your Mac with the Time Machine, it’s too bad. But, you can still downgrade to the previous OS version. To do this, you will need to create a bootable installer of macOS Catalina.

    1. If you’re reading this before macOS Big Sur ships, you can go to the App Store and search for Catalina, then download it. Quit the installer, if it tries to install the OS.
    2. If your Mac already runs macOS Big Sur, download the macOS Catalina here.
    3. Get an external hard drive that has at least 12 GB of available storage and plug it in your Mac.
    4. Launch the Disk Utility app and erase your hard drive selecting Mac OS Extended format.

    Now, it’s time to transfer your Catalina installer to your hard drive:

    1. Open Terminal (Applications > Utilities).
    2. Paste this command and press Enter:

    sudo /Applications/Install\ macOS\ --volume /Volumes/MyVolume

    The downloaded file, which is your bootable Catalina installer, should be in your Applications folder. MyVolume is the name of the hard drive; if your hard drive or flash drive has a different name, replace MyVolume with the name of your hard drive.

    1. If prompted, enter your administrator password and press Enter again. Terminal won’t show anything when you type your password.
    2. Follow the instructions that appear in the Terminal.
    3. When Terminal says “done”, your hard drive should have the same name as the installer you downloaded (for example, Install macOS Catalina).

    Quit Terminal and eject the hard drive.

    Install macOS Catalina

    Now, you can roll back from macOS Big Sur using the bootable installer.

    • Plug your hard drive (which is now your bootable installer) into your Mac.
    • Open System Preferences > Startup Disk. Choose your bootable installer as a startup disk and press Restart.
    • Your Mac should start up to macOS Recovery.
    • Make sure your Mac has an internet connection to download firmware updates (you can use the Wi-Fi menu in the menu bar).
    • In the Utilities window, select Install macOS.
    • Click Continue and follow the on-screen instructions.

    Your Mac will then start installing macOS Catalina and will restart when it’s done.

    Mac runs slowly after the update?

    If your Mac is slow after the update, but you don’t want to perform this lengthy process and revert to the previous OS, you could try a quick solution. CleanMyMac X has a helpful Maintenance feature that could fix all possible problems on your Mac.

    1. Open CleanMyMac X.
    2. Go to the Maintenance module.
    3. Press View All 9 Tasks.
    4. Check the boxes next to the first four options and also select Rebuild Launch Services.
    5. Press Run.

    Wait till CleanMyMac X runs the set of fixes to speed up your Mac.

    Reverting to the previous macOS may seem like a terrifying task. But if you open this article on your phone and follow the instructions, it will be much easier and faster. Don’t forget to clear your Mac before the backup – you will save a lot of free space and remove old clutter that slows down your machine.

    CleanMyMac X CleanMyMac X
    CleanMyMac X

    Your Mac. As good as new.