There are a number of reasons you may want to reinstall macOS. It could be that your Mac is misbehaving, and nothing you’ve tried will fix it. Sometimes, reinstalling macOS is the only way. Or it could be that you have installed the most recent version and discovered you don’t like it or it’s not compatible with some apps you need to use. Or maybe you need to test software on an older version of macOS and need to reinstall it on an older Mac. Whatever the reason, we’ll show you how to do it.
But first, let us show you the options you have:
| Reinstall option | What it does | When to choose | How to do it |
| Standard reinstall | Replaces core operating system files while keeping your user data, documents, and installed apps intact | Your Mac feels sluggish and crashes often A recent update failed or corrupted system files You need the fastest solution | Boot into recovery mode > Reinstall macOS |
| Clean install | Completely wipes your startup drive, erasing all data, apps, and settings, then installs a fresh copy of macOS | Severe software corruption Persistent malware Selling/giving away MacBook | Erase your Mac > Reinstall macOS |
| Downgrading macOS | Replaces your current operating system with a previous, older version of macOS | Apps you rely on break on a new macOS A new macOS extremely slows down your Mac | Use a pre-upgrade Time Machine backup or install macOS from a bootable installer |
Whichever option you choose, it’s a good idea to clear out any junk files first, so you’re not installing a macOS on unstable foundations. The easiest way to clean out junk files is to use CleanMyMac. Its Cleanup feature scans your Mac for junk files and allows you to delete them at the click of a button. You can test CleanMyMac for 7 days — get your free trial here.
How to reinstall macOS
The process for reinstalling macOS differs slightly for Macs running on Apple Silicon and Intel-based Macs. Choose the method that applies to your Mac. Before you start, you should back up your Mac, preferably using Time Machine. That way, if anything goes wrong, you will be able to easily restore your data.
Apple Silicon
- Shut down your Mac.
- Press and hold the power button until you see the Startup Options window.
- Click Options > Continue.
- When the macOS Utilities window appears, select Reinstall macOS.
- Follow the onscreen instructions.
Intel-based Mac
- Shut down your Mac.
- Press the power button while holding Command+R.
- Release Command+R when you see the macOS Utilities screen.
- Select Reinstall macOS.
- Follow the onscreen instructions.
How to do a clean reinstall of macOS on your Mac
A clean install means completely wiping all data and settings from your Mac before you reinstall macOS. If a normal reinstall doesn’t solve the problems you were having, or you plan on installing an older version than the one currently installed, you’ll need to do a clean install.
If you haven’t backed up your Mac using Time Machine already, you should do that now.
The way you do a clean install differs depending on what kind of Mac you have and which version of the OS you’re using.
Apple Silicon Mac or Intel Mac with T2 security chip
- Click on the Apple menu and select System Settings > General > Transfer or Reset, and then Erase All Content and Settings.
- Type in your password.
- You’ll be reminded to do a backup with Time Machine, but as you’ve done that already, you can skip that step.
- You’ll see a window showing you what will be deleted and prompted to log out of your Apple Account.
- Once you have logged out, you’ll see a final warning. If you’re happy to continue, click Erase All Content and Settings.
- Your Mac will restart, and it will do so as a brand-new Mac. You can then go ahead and reinstall macOS from macOS Utilities.
Intel Mac without a T2 chip
- Restart your Mac in recovery mode as shown above.
- Select Disk Utility.
- Choose your startup disk and click Erase.
- Follow the steps on the screen to format and name the disk and erase it.
- Once the disk is erased, quit Disk Utility to return to the macOS Utilities window.
- Select Reinstall macOS.
- Follow the onscreen instructions to reinstall macOS and set up your Mac.
How to install an older version of macOS
If you want to install an older version of macOS than the one you’re currently running, the easiest way to do it is to restore your MacBook from a pre-upgrade Time Machine backup. You will need to boot into recovery mode and choose Restore from Time Machine backup. Then, follow the onscreen instructions to complete the downgrade.
If you do not have a backup, you’ll need to download the installer from Apple and create a bootable install disk. Before you do that, you’ll need to check that the version of macOS you want to install is compatible with your Mac. For example, Macs with Apple Silicon will only run macOS Big Sur and later, so you can’t install Catalina, Mojave, or anything earlier on them.
Apple keeps downloadable installers for old versions of macOS on the App Store, but they’re not easy to find. Fortunately, Apple keeps a list of the links on its website here. In the same article, you will find the command you'll need to run to get macOS Tahoe installer, which cannot be downloaded via the App Store.
When you’ve downloaded the version of macOS you need, quit the installer when it launches. The install file will now be in your Applications folder. To create a bootable installer, you’ll need a USB stick formatted as macOS Extended or APFS and with at least 16 GB of space.
Plug in the USB stick and open Terminal from Applications > Utilities.
The Terminal command you need depends on the version of macOS you want to install and the name of your USB stick. The command below is an example where we are installing macOS Tahoe on a USB stick called MyInstaller. Change ‘Tahoe.app’ and ‘MyInstaller’ to reflect the version of macOS you’re creating an installer for and the name of your USB stick.
sudo /Applications/Install\ macOS\ Tahoe.app/Contents/Resources/createinstallmedia —volume /Volumes/MyInstaller
Apple has a full list of Terminal commands for different versions of macOS here.
Once you’ve created the bootable installer, select it as your startup disk in System Settings / System Preferences > General and restart your Mac. When it restarts, follow the instructions on the screen to install macOS
Most of us never have to reinstall macOS, but if you do, following the steps above for the situation that applies to you will make sure your Mac is back up and running in no time.
