Erasing the drive takes about five minutes and very few people mess up that part of the process. What people tend to get wrong is the sequence of actions around the erase, and unlike the erase itself, the sequence can never be fixed after it has happened.
Every meaningful answer on this page splits depending on your computer model, so work out the model before anything else. Open the Apple menu, click on About This Mac, and read the chip or processor line. There are three generations in circulation and they behave completely differently when erased. Apple Silicon computers (any machine with an M-series chip) automatically encrypt their storage in hardware. Intel Macs from roughly 2018 to 2020 carry the T2 security chip and do the same. Intel Macs from 2017 and earlier have neither the M-series chip nor the T2 chip, and on those older systems an erase means something much weaker than most people assume.
This information decides three different things: which type of erase you should use, whether any of your data could be recovered once it has been erased, and whether its drive is worth sending to us if you later realise you wiped the wrong one. It takes about thirty seconds of checking, and it prevents most of the bad outcomes described below.
The first thing to do is get those files off and get them somewhere you have actually opened. A Time Machine disk that has never had a backup restored from it is an assumption with a schedule attached, so mount that disk and go through and find the folders you care about by their names on the screen. Then make sure to capture all of the other stuff that lives outside the obvious places too: the desktop, Downloads, local mail archives, licence key notes you typed years ago, and anything else in a synced folder for a service that you will be signing out of.
The second thing to do is detaching the computer from yourself, and this is the step that creates the awkward telephone calls. Sign out of Apple ID, iCloud and Messages, and turn Find My off. If you are using an Apple Silicon or T2-based computer, then leaving Find My on will leave Activation Lock on. This means when the new owner gets to the setup assistant, they will be prompted for your Apple ID password before being able to continue, and they will be left with a paperweight until you provide it. A wipe doesn't remove the Activation Lock, since it lives on Apple's servers and not on the disk. Deauthorise the machine in either the Music or iTunes app if you've ever purchased anything, and unpair any Bluetooth keyboards, mice or trackpads so that they won't follow the Mac out of the house.
To wipe an M-series Mac, or an Intel-based model with a T2 chip, the whole operation is one menu choice. Open System Settings, select General, then Transfer or Reset, and click on Erase All Content and Settings. This will sign out of Apple services, erase the data and the settings, and leave the machine sitting at the setup assistant screen. No manual reinstall of macOS is needed, and none should be attempted.
Understanding what is happening underneath will help you to understand why nothing ever comes back. Storage in these machines has been encrypted since it left the factory, and the keys are stored in the Secure Enclave. Erasing does not work by writing over your files one by one. It throws away the keys, and the flash storage is left holding ciphertext that nothing anywhere has any means of turning back into a photograph. That is genuinely final: not difficult, not expensive, not a matter of finding the right laboratory. Excellent news when you are selling the machine on. A very short conversation if you have just wiped the wrong one.
Without a T2 there is no single control, so everything runs through macOS Recovery. To get into it, restart your machine while holding Command and R. When Disk Utility opens, go to the View menu and switch on Show All Devices. This will display the physical drive itself as well as the volumes stored on it. It is the drive at the top level (the device) that needs to be erased, not the volume below it. If you have reasonably modern hardware choose APFS; Mac OS Extended (Journaled) is only for genuinely old computers. Afterwards close Disk Utility and select Reinstall macOS from the Recovery menu.
Two things you should know about before proceeding. The reinstall downloads macOS over the internet and is not a five-minute job, so make sure you have a connection that will hold up, and keep the charger plugged in throughout. The more important point is how much data remains after the erase. If FileVault was never switched on, erasing an Intel Mac is not destruction. The references to the files are deleted, but the files themselves still sit in their original locations on the drive, waiting to be overwritten, and any competent lab will recover a large portion of them. That may be a relief if you wiped the wrong computer. However, it is a real problem if you have already handed the computer to a buyer you have never met. To protect yourself, either turn on FileVault and allow the encryption to complete before erasing anything, or remove the disk altogether and have it destroyed.
Eventually the question will change from "how can I erase this?" to "how can I make sure no one ever reads it?": a cupboard of retired hard drives, a practice clearing out closed files, a server that's been sitting in a storeroom since the last migration. A quick format will achieve nothing here at all; the drive walks out of your building just as readable as it was when it went in. On a mechanical hard drive there are really only two methods that stand up. The first is completely overwriting every addressable sector of the disk, which takes hours per drive and only works if the drive is still healthy enough to accept every write. The second is physically destroying the platters themselves, and it is the platters that matter. Drilling through the case does not qualify, since the drill bit comes into contact with only a small fraction of the recording surface, and anything the bit missed stays readable by anyone who has a bench and some patience.
Solid-state media does not follow those rules, and that is where most people come unstuck. A controller decides for itself where any particular write physically lands, and every SSD and memory card also sets aside some reserve capacity that you cannot reach with any command, so even blocks you are confident you have overwritten may still be sitting intact in that reserve. There are three methods that do work: the drive's own built-in hardware secure erase, a cryptographic erase on media that was encrypted from new, or reducing the device to particles small enough to defeat chip-level reading, where the material genuinely warrants it. None of these is offered here, because this is a laboratory, not a disposal contractor, and pretending otherwise would not help you. If you need to dispose of any quantity, use a company that shreds to a published standard and gives you a certificate an auditor will accept. The only promise made about devices sent in for recovery is that they are returned to you, or destroyed securely on your written instruction once the work is finished. Nothing is ever thrown away.
A large number of the people who find their way to a page like this are not selling anything to anybody. They're looking for a reset because the computer has already stopped working properly (it freezes before it even gets to the desktop, the internal storage has gone missing from Disk Utility, or there's a folder on the screen with a question mark blinking in the middle). A reset does nothing to address any of these. In fact, a reset is the most damaging thing you can do at that point, as it will destroy the last remaining copy of your data and leave the underlying fault completely untouched.
Put it down instead. Many older iMacs and MacBooks have a hard drive or SSD that comes out by removing a couple of screws or a clip, and once it is removed the drive can be read on a bench, whether or not the computer will ever start again. First get a quote, either by calling us on 0800 689 0668 or by completing our free online diagnostic. Then post the drive, insured and tracked, to Guildford Data Recovery, Building 2, Ground Floor, Guildford Business Park, Guildford, GU2 8XH, or bring it to the Guildford lab yourself, which takes about forty minutes from Bracknell along the A322 and the A3, and hand it to reception Monday to Friday, 9am to 5:30pm, with no appointment needed. There is no collection service and no counter in Bracknell, so the whole thing comes down to one parcel and one call to 0800 689 0668. The free diagnosis is finished 2 working days after booking in, and a single hard drive or SSD is £300 + VAT, confirmed in writing before anything is chargeable.
The one honest no on this page is storage soldered into the logic board, which is how every Apple Silicon machine and many ultrabooks are built. There's nothing to unclip and nothing to post, and if the board itself has failed, all of your files go down with it. If you're unsure which kind of storage you've got, please give us a call first. It's better to tell you now than after somebody has charged you to find out.
First copy off anything important, second sign out, third erase. The erase takes five minutes, and it is the only step that can't be redone. Everything expensive on this page comes from doing one of the two steps before it out of order, or not doing it at all.
Free diagnostic completed within 2 working days of booking in your device, then one fixed written quote, and in most cases you only pay if we recover your data. Cards and USB sticks £250 + VAT, and any single drive or SSD £300 + VAT.