How to Wipe/Factory Reset your Mac Before Selling

Before transferring the ownership of your Mac to someone else, it’s important that you first perform a complete wipe of the hard drive and do a fresh install of macOS. Doing this will prevent the new owner from accessing any of your files and personal information. This article will guide you through the process step by step.
Prepare your Mac for sale in five easy steps:

Back up the Hard Drive

Deauthorize

Sign Out

Wipe the Hard Drive

Fresh macOS Install

Back up the Hard Drive
Backing up your data before wiping a computer hard drive is a necessary step. You can back up to a different machine or simply to an external hard drive, whichever works best for you. If you like, you can even have multiple backups in the event you run into technical difficulties with one of them.
Using the application Time Machine is an easy way to keep a backup of your data and files on external hard drive, and it even let’s you use multiple ones should you need to. However, if your new computer is also a Mac you need to be careful not to let Time Machine overwrite the backup from your old one, or it will overwrite all your stored files and data.
If you don’t want to use Time Machine, there are other options; SuperDuper or Carbon Copy Cloner are both tried and true. They can make a perfect clone of your Mac’s hard drive onto an external one, which can even be used as a handy boot drive for your Mac.
Deauthorize
It’s important to note that you can only connect 5 devices to a single iTunes account. Deauthorizing your old Mac (and any old Apple devices you plan to sell or pass along) is a good way to make sure you’re always able to connect your new devices. It also helps prevent any conflicts that may arise if the new owner tries to download applications that are tied to your Apple ID.
The deauthorization process for iTunes is simple; launch iTunes and navigate to the ‘Account’ option in the menu. A drop-down menu will appear, click ‘Authorizations’ and another menu will pop out. In it, simply click ‘Deauthorize this Computer’, enter your Apple ID and password when prompted, and click ‘Deauthorize’.
Sign Out
You should sign out of iCloud and iMessage before wiping your Mac, and this is also very easy to do.
For iCloud, click on the Apple in the upper left corner and go into ‘System Preferences’. Select iCloud, click ‘Sign out’, and confirm the removal of data. Your iCloud data will remain intact and will still be accessible from any device where you sign in with an Apple ID.
For iMessage, open up the Messages application. In the top left, click ‘Messages’, then ‘Preferences’. Select your iMessage account, click ‘Sign out’, and you’re done!
Wipe the Hard Drive
WARNING: Before you proceed with this step, please make absolutely sure all the data you want to keep is safely backed up, as there’s no going back after the wipe is done.
Navigate to the Apple menu in the upper left corner and select ‘Restart’. Let your computer shut down, and as it starts booting up hold down Command + R on the keyboard until you see the ‘Recovery Mode’ screen.
Once there, select ‘Disk Utility’ and then ‘Continue’. You’ll see your Mac’s startup disk in the left-hand sidebar (it’ll be named ‘Macintosh HD’ or alike). Select it and click the ‘Erase’ tab on the right-hand side.
There’s an option you can choose if you’re worried someone will attempt a recovery of the data you’re about to erase. By clicking ‘Security Options’ you can select a higher security level for your wiped data, however this will slow the erasure process down considerably. Once you’re happy with your selection, click ‘Erase’ and the process will begin.
When the wipe has completed, select ‘Disk Utility’ followed by ‘Quit Disk Utility’.
Fresh macOS Install
You’ll now be returned to the ‘Recovery Mode’ screen. Here, you should click ‘Reinstall macOS’ and then ‘Install’. Your Mac will proceed to download (unless you’re installing from a disk or drive) a new copy of macOS and then install it. Continue until you’re asked for your Apple ID and password. This is where you should stop, as the setup will be continued by whomever is taking over your old machine.
You should now have a completely wiped Mac, with a fresh install of macOS. It’ll have all your personal information, data, and applications erased from it and be ready for a new owner. If you need more information or technical support regarding wiping your Mac’s hard drive, you can visit the Apple Support Website.