How to Update/Reinstall macOS Without Losing Data

Updated by Daisy on Sep 22, 2022
Written by Tracy King
  | Computer Instruction

This page covers the full process of how to update and install the latest macOS Big Sur, Catalina, Mojave, etc. on Mac without losing any data. If you need a detailed guide, follow through this page to get the desired macOS installed on your computer now:

Workable Solutions Step-by-step Troubleshooting
Phrase 1. Preparations 2GB+ memory and 9GB+ storage space left on Mac > 45% + battery > Connect to internet...Full steps
Phrase 2. Change a USB port Start Mac from macOS Recovery > Select "Reinstall macOS" > "Continue"...Full steps
Phrase 3. Recover Lost Data After macOS installation, run EaseUS Mac data recovery software > Scan and recover lost data...Full steps

Applies To: macOS Big Sur, macOS Catalina, macOS Mojave, macOS High Sierra, macOS Sierra, or earlier Mac operating systems

Reinstall macOS Mojave, High Sierra, Sierra without losing data

The need to update or reinstall your macOS always follow the release of a new operating system, the slow performance of your Mac, or a system crash. When it comes to reinstalling macOS, users biggest concern is losing data on their computer.

The good news is that, if you follow the instructions strictly to update your Mac Operating System, the chance to lose data on your Mac is quite slim, since a reinstallation just needs to create a new copy of the OS, your existing files stored on your Mac won't be lost. Thus, as long as you don't choose to erase your startup disk during the reinstallation, you won't lose files. However, you know what "Slim" means - it's not 100% safe and is still at the risk of losing some data.

Then how to reinstall macOS without any data loss? To provide a double guarantee to the precious data on your Mac, you can make a copy of the files on your Mac before you perform the reinstallation, or equip your Mac with a data recovery tool that can rescue your data after the reinstallation.

Preparations you Need to Make Before You Reinstall macOS

To reinstall macOS on your computer smoothly. Follow the tips below to prepare your Mac ready for the new macOS update now:

  • Leave at least 2GB memory and 8.8 GB storage space on your Mac
  • Leave at least 45% battery on your Mac
  • Connect Mac to the internet or WiFi
  • Update your Mac Apps to the latest versions
  • Backup all your personal data and even create backups for your present Mac data through Time Machine

Remember to back up your Mac to an external hard drive for preventing system update failure or unexpected troubles from happening. Then follow the detailed guide below to reinstall Mac OS via macOS Recovery mode, which enables you to reinstall macOS, restore your files from Time Machine, repair or erase a disk, and more.

How to Update & Reinstall macOS Without Losing Data

*Print this page or open this page on another device so you can refer to it later.

Step 1. Start up your Mac from macOS Recovery

  • Turn on your Mac and immediately press and hold "Command + R", "Option + Command + R", or "Shift + Option + Command + R".
  • Release the keys when the Apple logo, a spinning globe, or a pop-up for a firmware password appears.

Step 2. Select "Reinstall macOS" from the Utilities Window and click "Continue".

Step 3. Follow the onscreen instructions to select the hard drive you want to install the OS on and start the installation.

Step 4. Don't put your Mac to sleep mode or close its lid during the installation. It's normal to see your Mac restart several times or the screen is white while you reinstall the Mac OS. Just wait patiently for the process to finish.

How to Update & Reinstall Mac OS Without Losing Data

If data loss occurred after you reinstalled macOS, you can follow the next part to recover your missing files.

Recover Lost Data After macOS Reinstallation

If you have backed up your Mac before the reinstallation, you can retrieve your data from Time Machine, an external hard drive, or somewhere else, depending on the way you used to make the backup. If you haven't created any backups for your Mac, then you'll need the professional Mac data recovery software tool - EaseUS Data Recovery Wizard, to perform data recovery. With the help of this tool, you can easily recover the data lost due to macOS reinstallation:

 Download for Win Recovery Rate 99.7%
 Download for Mac Trustpilot Rating 4.6

Note: To guarantee a high data recovery chance, install EaseUS data recovery software on another disk instead of the original disk where you lost files. 

Step 1. Launch EaseUS Data Recovery Wizard on your Windows 11, Windows 10, Windows 8, or Windows 7 computer. Select the disk partition or storage location where you lost data and click "Scan".

select the disk on Windows  to scan

Step 2. This recovery software will start scanning the disk to find all lost and deleted files. When the scan process completes, click "Filter" > "Type" to specify lost file types.

choose the recovered data type

Step 3. Preview and restore lost Windows files. You can double-click to preview the scanned files. Then, select the target data and click the "Recover" button to save them to another safe spot in the PC or an external storage device.

recover windows 10 lost data

There are lots of data recovery tools available. But EaseUS Data Recovery Wizard, one of the best Mac data recovery tools, is our pick. It fully supports all macOS systems including the newest Big Sur, Catalina, Mojave, High Sierra, Sierra, EI Capitan, Yosemite etc. It allows you to restore all lost data with simple clicks. Office files, music, videos, emails or other archives can all be restored on your own. 

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