With Monterey being the latest version of macOS, many Mac owners have left Big Sur behind. But if your machine isn’t one of the Macs that are compatible with Monterey, then Big Sur could be the newest operating system you can run.
In most cases, you should stick with Big Sur, but there are still reasons why you might want to downgrade macOS to Catalina. If you find yourself in that position, here’s how to do it.
Before we start
If you’re downgrading to Catalina because of performance issues with your Mac, give MacKeeper a try first. It offers a range of security, optimization and cleaning features, which could be what’s causing your problems. You can download it now and get one free fix using each tool. That could be just what you need.
When and why should you downgrade Big Sur to Catalina?
In general, you should always use the latest version of macOS you can run. As well as giving you access to the newest features and apps, you’ll get security updates from Apple for longer. Eventually, it drops support for older Macs and operating systems. That could leave you vulnerable to malware.
Nevertheless, there are times when it might be reasonable to downgrade to an earlier version of macOS like Catalina:
- To fix problems: Big Sur has been around a while, so it should be stable on your Mac. But if you’re still experiencing problems with Big Sur, downgrading could solve them.
- To run old hardware or software: If you have old peripherals or apps that no longer run on Big Sur, downgrading to Catalina might be your only option to get them working again.
- For performance reasons: You shouldn’t have any speed problems when you upgrade to Big Sur, but if you do, then going back to Catalina might be worth it.
Back up your data
Before you downgrade to Catalina from Big Sur, you should back up any important data on your Mac. Of course, if you’re happy to lose everything stored on your Mac, then you don’t need to worry about it.
There are four key ways you can back up the data on your Mac:
- Manually copy files to an external location like a USB drive
- Back up using Time Machine
- Clone your entire Mac hard drive
- Store your important files in iCloud
Check out our full guide to backing up your Mac for more information.
How to downgrade Big Sur
Once you’ve secured any important data, there are a couple of ways to go from Big Sur back to Catalina. One uses macOS’s own Time Machine feature, while the other requires you to create a bootable USB drive.
Downgrade Big Sur using Time Machine
If you’ve made a backup of your Mac using Time Machine, then good news: you can use that to restore your Mac to Catalina. Nice and simple!
Erase your Mac’s system disk
To go back to Catalina using Time Machine, you should start by erasing everything that’s stored on your main system drive.
You can erase your Mac in a few easy steps:
- First, you need to erase and format your Mac. Start by turning it off
- Now power it back up, holding down the Command+R keys as it starts up
- You’ll see the macOS Utilities window. Choose Disk Utility
- Click Continue, then choose Startup Disk
- Click Erase, and choose the APFS file format
- Finally, select GUID Partition Map, and Confirm
Restoring your Mac using Time Machine
With a clean disk drive, you can go ahead and reinstall Catalina.
Downgrade Big Sur with Time Machine like this:
- Restart your Mac, holding down the Command+R keys while it reboots
- In the macOS Utilities window choose Restore From Time Machine Backup, and click Continue
- Select your Time Machine backup disk in the next window, and click on your most recent backup before installing macOS Big Sur
- Choose a destination disk — all your backup contents will be stored there
- Press Restore, then Continue
Provided everything goes to plan, when your Mac restarts, it should be back to Catalina again.
Downgrade to Catalina using a bootable USB drive
Using Time Machine makes downgrading Big Sur much easier, but if that’s not an option for you, don’t worry. You can still revert to Catalina; it’s just going to take a bit longer.
Create a bootable drive for Catalina
Before you can downgrade to Catalina, you’ll need to create a suitable USB drive for the operating system.
Here’s how to create a bootable USB drive for your Mac:
- Start by connecting an external drive with more than 12GB of storage to your Mac
- Next, you’ll need to download a copy of macOS Catalina from the App Store
- Now, open Disk Utility from Applications > Utilities
- Find your external drive in the list, then select Erase, choosing the Mac OS Extended format
- Once that’s finished, launch Terminal from your Utilities folder. Type or paste in the following command, and press Enter: sudo /Applications/Install\ macOS\ Catalina.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume
- Enter your admin password
- Follow the instructions in Terminal, then close it down, and eject your USB drive
Related reading: How to Create a Bootable Installer for macOS
Prepare your Mac to boot from USB
If your Mac uses a T2 chip, you’ll need to allow it to boot from USB. Check out Apple’s list of T2 Macs, if you’re in any doubt.
To get your Mac ready to boot from an external drive, do the following:
- Put your Mac in Recovery Mode by holding Command+R as it starts up
- Select Access Utilities > Startup Security Utility
- Enter your firmware password. This is not the same as your admin or Apple ID password, so make sure you know what it is before going any further
- Click the box next to Allow booting from external media
- Wait for the process to complete
Installing Catalina from USB
Now it’s time to use your newly created bootable USB drive to downgrade back to Catalina.
Follow these steps to install Catalina on your Mac:
- Connect your external drive to your Mac
- In System Preferences, select the Startup Disk tab
- Now select your external drive as the startup disk, and click Restart
- Your Mac should start up in Recovery Mode. Choose Install macOS, and click Continue
- Now follow the normal installation process, and your Mac should restart with Catalina
Looking beyond Catalina
As we said earlier in this article, you shouldn’t normally downgrade macOS — not unless you really need to. Long term, you should consider whether it’s a good idea. Although Apple doesn’t have a clearly defined policy for when it stops supporting older Macs, it does eventually drop security updates for them.
So if you’re holding on to Catalina because of some old piece of hardware or software, you should perhaps be thinking about finding an alternative, rather than downgrading Big Sur. In the short term, though, it can be a quick solution to your problems, and hopefully this guide has shown you the way.