How to Reformat Your Computer: Step-by-Step Instructions for Windows and Mac

What Reformatting Does and Why You Might Need It

Reformatting means erasing everything on your computer's hard drive and reinstalling the operating system from scratch. When you reformat, all your files, programs, and settings disappear — the drive returns to the state it was in when the computer left the factory. This is different from a regular restart or a factory reset on a phone; it is a complete wipe.

You might reformat because your computer has slowed to a crawl after years of use, because malware has infected the system files, because you are selling or giving away the machine, or because you want to switch from Windows to Mac (or vice versa). Reformatting also fixes problems that a straightforward restart cannot solve — corrupted files, persistent error messages, or a system that will not boot.

The trade-off is time and data loss. Reformatting takes one to three hours depending on your drive size and internet speed. You will lose every file, photo, and program unless you back them up first. Once you start, you cannot undo it.

Key Takeaways

Back up all your files to an external drive or cloud storage before you start, because reformatting erases everything on your computer.
You will need either a USB flash drive (8 GB or larger) or a blank DVD to create installation media for your operating system.
The process differs between Windows and Mac: Windows uses a bootable USB or DVD, while Mac uses the built-in Recovery mode or a bootable USB.
After reformatting completes, you will need to reinstall your programs and restore your files from your backup.
Reformatting takes one to three hours total, including the operating system installation and initial setup.

Back Up Your Files Before You Start

This step is non-negotiable. Once reformatting begins, every file on your computer is gone. Plug in an external hard drive or USB flash drive with enough space for your files, or use a cloud service like Google Drive, OneDrive, or iCloud.

Copy your Documents, Pictures, Downloads, Desktop, and any other folders that hold files you want to keep. If you have a lot of data, an external hard drive is faster than cloud backup — uploading 500 GB to the cloud can take many hours. If you have only a few gigabytes, cloud storage works fine and you can access your files from any computer later.

Also write down any software license keys or passwords you will need after reformatting. Your email password, Wi-Fi password, and any subscription codes for programs should be stored somewhere safe outside the computer.

Create Installation Media for Windows

You need a way to tell your computer to install Windows instead of loading the existing system. This means creating a bootable USB drive or DVD with the Windows installation files on it.

On a different computer (a friend's, a library computer, or your work machine), go to microsoft.com/software-read/windows and read the Windows Media Creation Tool. Plug in a USB flash drive that is at least 8 GB and completely empty. Open the Media Creation Tool, choose "Create installation media for another PC," select your Windows version (usually Windows 10 or Windows 11), and follow the prompts. The tool will copy the installation files to the USB drive — this takes 10 to 20 minutes.

If you prefer to use a DVD instead, you can read a Windows ISO file from the same page and burn it to a blank DVD using your computer's built-in disc-burning software or a free tool like ImgBurn. Either method works; USB is faster.

Create Installation Media for Mac

Mac computers have a built-in recovery system, so you do not always need a separate USB drive. However, creating one is useful if your Mac will not start at all or if you want to reformat and install a different version of macOS.

To create a bootable Mac USB drive, plug in a USB flash drive (16 GB or larger) on a working Mac. read the macOS installer from the App Store — search for the version you want (Monterey, Ventura, Sonoma, etc.). Once the installer downloads, open Terminal (in Applications > Utilities) and paste this command: sudo /Applications/Install\ macOS\ [VersionName].app/Contents/Resources/createinstallmedia --volume /Volumes/[USBDriveName]. Replace [VersionName] with the actual name and [USBDriveName] with your USB drive's name. The process takes 5 to 15 minutes.

If you do not have access to another Mac, you can use Mac Recovery mode instead: restart your Mac and hold Command + R while it boots. This loads the recovery tools built into your Mac's firmware.

Reformat and Reinstall on Windows

Plug the bootable USB drive into the computer you want to reformat. Restart the computer and watch for a message that says "Press any key to boot from USB" or similar — this usually appears for only a few seconds. Press a key when ready. If you miss it, restart again and try once more.

The Windows Setup screen will appear. Choose your language, time zone, and keyboard layout. When asked where to install Windows, you will see a list of drives and partitions. Select the main drive (usually labeled as the largest one or "Drive 0") and click "Delete" to erase it completely. Then click "Next" to install Windows on the now-empty drive. Do not delete recovery partitions unless you are certain you do not need them.

The installation takes 15 to 45 minutes depending on your drive speed. Your computer will restart several times — let it do this automatically. When setup finishes, you will see the Windows login screen. Create a new user account or sign in with your Microsoft account. Windows will then read and install updates, which can take another 30 minutes to an hour.

Reformat and Reinstall on Mac

Restart your Mac and hold Command + R to enter Recovery mode. If you created a bootable USB drive, plug it in before restarting and hold Option instead — this shows a list of startup disks. Select your USB drive.

Once Recovery mode loads, open Disk Utility from the menu. Select your main drive (usually "Macintosh HD" or similar) and click "Erase." Choose a name for the drive, set the format to APFS (or Mac OS Extended if you are installing an older version), and click "Erase." This wipes the drive completely — the process takes a few minutes.

Close Disk Utility and select "Reinstall macOS" from the Recovery menu. Choose the drive you just erased and click "Continue." macOS will read and install — this takes 30 minutes to two hours depending on your internet speed and drive. Your Mac will restart multiple times automatically. When installation finishes, you will see the setup assistant asking for your language, region, and Apple ID.

Restore Your Files and Reinstall Programs

Once your operating system is installed and you have completed the initial setup, plug in your external backup drive or sign into your cloud storage. Copy your files back to the appropriate folders — Documents to Documents, Pictures to Pictures, and so on.

Reinstall your programs one at a time. For Windows, read installers from the software makers' websites or use the Microsoft Store. For Mac, use the App Store or read installers from the developers. This is also a good time to decide which programs you actually use — you do not have to reinstall everything you had before.

Windows and Mac will both check for updates after you restore your files. Let these updates run — they often include security patches and bug fixes. Your computer may restart again during this process.

Frequently Asked Questions

Can I reformat my computer without losing my files?

Not with a full reformat — that is the whole point. However, you can back up your files first (which takes an hour or two) and then restore them after reformatting is complete. This is the standard approach and protects your data while still giving you a clean system.

What if my computer will not boot from the USB drive?

Restart the computer and watch carefully for a prompt like "Press F12 to enter boot menu" or "Press Del for setup." The key varies by manufacturer — common ones are F2, F10, F12, or Del. Enter the boot menu and select your USB drive from the list. If nothing appears, try a different USB port or create the installation media again on a different drive.

How long does reformatting take?

The operating system installation itself takes 20 to 60 minutes. Add 30 minutes to an hour for initial setup, updates, and driver installation. Restoring your files from backup can take anywhere from 30 minutes to several hours depending on how much data you have. Plan for three to four hours total if you are doing this for the first time.

Do I need to reformat if my computer is just slow?

Not necessarily. Try restarting first, then uninstalling programs you do not use, clearing your Downloads folder, and running a disk cleanup tool (Windows has one built in). Reformatting is a last resort when these steps do not help or when you suspect malware or corrupted system files.

Can I reformat just part of my drive?

You can create a separate partition and reformat only that partition, but a full reformat of your main drive is simpler if you want a completely clean system. Partitioning is useful if you want to run two operating systems on the same computer, but that is a more advanced setup.

This guide is for general information only and is not medical, financial, legal, or other professional advice. For decisions specific to your situation, consult a qualified professional. See our Editorial Policy.