Introduction

A clean installation of macOS involves completely erasing your Mac's storage drive and installing a fresh copy of the operating system. Unlike a standard update or upgrade, a clean install removes all your applications, settings, and data, giving you a completely fresh start.

This comprehensive guide will walk you through the entire process of performing a clean installation of macOS, from backing up your data to setting up your fresh system.

Caution: A clean install will erase all data on your Mac's startup disk. Make sure to back up all important files before proceeding.

When to Do a Clean Install

A clean installation is not always necessary, but it can be beneficial in several situations:

Persistent performance issues: If your Mac has become noticeably slower over time and standard troubleshooting hasn't helped.
Storage problems: When you're experiencing disk space issues that disk cleanup utilities can't resolve.
Software corruption: If you're experiencing frequent crashes, freezes, or other unexplained behavior.
Malware concerns: When you suspect your system may be compromised.
Major macOS upgrade: When upgrading to a significantly newer version of macOS (e.g., several versions ahead).
Selling or giving away your Mac: To ensure all your personal data is removed.

A clean install can often resolve issues that have accumulated over time due to software conflicts, remnants of uninstalled applications, and system fragmentation.

Prerequisites

Before performing a clean installation, you'll need to prepare a few things:

A complete backup of all your important data
A bootable macOS installer on a USB drive (8GB or larger)
Your Apple ID and password
Licenses and installation files for your applications
A stable internet connection
At least 1-2 hours of time (depending on your internet speed)

Backing Up Your Data

The most important step before a clean install is to create a comprehensive backup of all your data.

Using Time Machine:

Connect an external storage device with sufficient space
Go to System Settings > Time Machine (or System Preferences > Time Machine in older versions)
Click "Select Backup Disk..." and choose your external drive
Click "Back Up Now" to create a complete backup

Important items to back up manually:

Documents, photos, and videos
Browser bookmarks and saved passwords
Email accounts and messages
Application settings and preferences
Application license keys and registration information
Contacts, calendars, and notes

Tip: Take screenshots of your important settings and create a list of installed applications to make the restoration process easier.

Creating a Bootable Installer

You'll need a bootable macOS installer to perform a clean installation. Here's how to create one:

Step 1: Download the macOS installer

Open the App Store
Search for the macOS version you want to install
Click "Get" or "Download" to download the installer
The installer will be saved to your Applications folder

Alternatively, you can download the installer from these direct links (opens App Store):

Step 2: Prepare your USB drive

Connect a USB drive (at least 8GB) to your Mac
Open Disk Utility (from Applications > Utilities)
Select your USB drive in the sidebar
Click "Erase" at the top of the window
Name the drive "macOS Installer" (or similar)
Select "Mac OS Extended (Journaled)" as the format
Select "GUID Partition Map" as the scheme
Click "Erase" and wait for the process to complete

Step 3: Create the bootable installer

Open Terminal (from Applications > Utilities)
Copy and paste one of the following commands, depending on your macOS version:

# For macOS Sonoma
sudo /Applications/Install\ macOS\ Sonoma.app/Contents/Resources/createinstallmedia --volume /Volumes/macOS\ Installer

# For macOS Ventura
sudo /Applications/Install\ macOS\ Ventura.app/Contents/Resources/createinstallmedia --volume /Volumes/macOS\ Installer

# For macOS Monterey
sudo /Applications/Install\ macOS\ Monterey.app/Contents/Resources/createinstallmedia --volume /Volumes/macOS\ Installer

Press Enter and provide your administrator password when prompted
Confirm the erasure of your USB drive by typing 'Y' and pressing Enter
Wait for the process to complete (it may take 20-30 minutes)

Note: For a more detailed guide on creating a bootable installer, see our dedicated tutorial: How to Create a Bootable macOS USB Installer.

Clean Installation Process

Now that you've backed up your data and created a bootable installer, you're ready to perform the clean installation.

Booting from the Installer

Connect your bootable USB drive to your Mac
Power off your Mac completely
Power on your Mac and immediately press and hold one of the following:
- On Intel-based Macs: Hold the Option (⌥) key
- On Apple Silicon Macs: Press and hold the power button until you see "Loading startup options"
Select your bootable installer (usually named "Install macOS [Version]")
Click the arrow or press Return to boot from the installer

Mac Startup Manager showing bootable installer selection

Using Disk Utility

Once booted into the macOS installer, you'll need to erase your Mac's startup disk:

From the macOS Utilities window, select "Disk Utility" and click "Continue"
In the sidebar, select your Mac's internal disk (not the individual volumes)
Click the "Erase" button in the toolbar
Set the following options:
- Name: Macintosh HD (or your preferred name)
- Format: APFS
- Scheme: GUID Partition Map
Click "Erase" and wait for the process to complete
When finished, click "Done"
Quit Disk Utility by selecting Disk Utility > Quit Disk Utility from the menu bar

Warning: This step will erase all data on your selected disk. Make sure you have a complete backup before proceeding.

Installing macOS

Now you can install a fresh copy of macOS on your erased disk:

From the macOS Utilities window, select "Install macOS" and click "Continue"
Click "Continue" on the welcome screen
Agree to the software license agreement
Select your erased disk (e.g., "Macintosh HD") as the installation destination
Click "Install" to begin the installation process
Wait for the installation to complete (this may take 30-60 minutes and your Mac will restart several times)

Note: During installation, your Mac will restart several times. Don't interrupt the process once it has begun.

After Installation

After the installation completes, you'll need to set up your Mac and restore your data.

Initial Setup

When your Mac restarts, you'll be guided through the macOS setup process:

Select your country or region
Choose your preferred keyboard layout
Connect to a Wi-Fi network
Choose whether to transfer information from another Mac, Time Machine backup, or set up as new
Sign in with your Apple ID
Set up Siri and other macOS features
Create a user account
Complete the setup process

Tip: For a clean installation, select "Don't transfer any information now" during the Migration Assistant step. You can restore specific items later from your backup.

Restoring Your Data

After setup, you can restore your data from your backup:

Option 1: Selective restoration (recommended for clean install)

Connect your backup drive to your Mac
Open Time Machine (from System Settings > General > Time Machine)
Click "Enter Time Machine"
Navigate to locate specific files or folders you want to restore
Select the items and click "Restore"

Option 2: Using Migration Assistant for specific items

Open Migration Assistant (from Applications > Utilities)
Select "From a Mac, Time Machine backup, or startup disk"
Select your Time Machine backup
Choose specific categories of items to transfer (e.g., Documents folder only)
Complete the migration process

Note: To maintain the benefits of a clean installation, consider restoring only essential data files and manually reinstalling applications rather than restoring everything.

Reinstalling Applications

Rather than restoring applications from your backup, it's generally best to reinstall them freshly:

Reinstall apps from the App Store by opening the App Store and going to the "Purchased" tab
Download and install third-party applications from their official websites
Apply any license keys or registration information you saved before the clean install
Configure application preferences as needed

Tip: For application settings and preferences, you can often selectively restore these from your backup by copying specific files from ~/Library/Preferences in your backup to the same location on your fresh installation.

Troubleshooting

If you're unable to boot from your installer USB:

Verify that your Mac supports the macOS version you're trying to install
Try a different USB port, preferably one directly on your Mac (not through a hub)
Reset the SMC and NVRAM/PRAM:
- SMC reset: Shut down, hold Shift+Control+Option+Power for 10 seconds, then release
- NVRAM reset: Restart and immediately hold Option+Command+P+R for 20 seconds
Try recreating the bootable installer using a different USB drive

If you don't see your internal disk in Disk Utility:

Make sure "Show All Devices" is selected from the View menu in Disk Utility
If using an external drive as your startup disk, make sure it's properly connected
Try booting into macOS Recovery (Command+R at startup) instead of the USB installer
If still not visible, your drive may have hardware issues and require service

If the installation fails with an error:

Make sure your Mac is connected to the internet during installation
Verify that the date and time are set correctly (in Terminal, use date command)
Try using a different macOS installer version
Ensure your Mac meets the minimum requirements for the macOS version
Try using macOS Recovery to install macOS instead of the USB installer

If data appears to be missing after restoration:

Check if the data is in a different location than expected
Verify that your backup is complete and accessible
Try using Time Machine's interface to browse and restore specific files
Check if the data might be in a different user account
For app-specific data, check the application's own backup or sync features

Frequently Asked Questions

How long does a clean installation take?

A clean installation typically takes 1-2 hours, including the installation process and basic setup. Restoring data and reinstalling applications can add several more hours, depending on the amount of data and number of applications.

Will a clean install improve my Mac's performance?

In many cases, yes. A clean installation removes accumulated system clutter, unused files, and potential software conflicts that may be slowing down your Mac. However, if your performance issues are hardware-related (like an aging SSD or insufficient RAM), a clean install may not fully resolve them.

Do I need to reinstall macOS if I'm selling my Mac?

Yes, if you're selling or giving away your Mac, you should perform a clean installation to remove all your personal data. Additionally, you should sign out of iCloud, iMessage, and other Apple services before erasing your disk. Apple provides a specific guide for what to do before selling or giving away your Mac.

Can I install an older version of macOS instead of the latest?

Yes, you can install any macOS version that's compatible with your Mac. However, note that you cannot install versions older than what your Mac originally came with. For security and compatibility reasons, we generally recommend installing the latest compatible version unless you have specific software requirements.

How often should I perform a clean installation?

There's no fixed schedule for clean installations. Some users do it annually as maintenance, while others only do it when experiencing significant problems. With modern macOS versions, routine clean installations are less necessary than they once were. Consider a clean install when you're experiencing persistent issues that other troubleshooting methods haven't resolved, or when upgrading to a significantly newer macOS version.

How to Clean Install macOS: Complete Step-by-Step Guide

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