Back up first, and check the backup
Erasing is irreversible and there is no undo. Before anything else, confirm you have a backup you could actually restore from: Settings → your name → iCloud → iCloud Backup shows the last successful backup date.
If that date is old, tap Back Up Now and wait for it to complete. Our backup check guide covers where to look for each backup type, and our computer backup guide covers making a more complete one.
The two different resets
Reset All Settings returns preferences, network settings, keyboard dictionary and Home screen layout to defaults while keeping all your apps and data. It is the right tool when something is misconfigured and you cannot find what.
Erase All Content and Settings is the factory reset: everything goes, and the phone restarts to the setup screen. Both live under Settings → General → Transfer or Reset iPhone.
Erasing the phone
Settings → General → Transfer or Reset iPhone → Erase All Content and Settings. iOS shows you what will be removed, offers to run a final iCloud backup first, and asks for your passcode and then your Apple Account password.
That Apple Account password step is Activation Lock being switched off. It is not optional and there is no way past it — which is the point of the feature.
Activation Lock, and why it matters
Find My includes Activation Lock: an erased iPhone still demands the original Apple Account credentials before it can be set up again. This makes a stolen phone useless, and it makes a phone sold without being properly erased useless to the buyer.
Always erase through Settings while signed in. If you erase some other way without turning off Find My, the phone stays locked to your account. Our guide to erasing before selling covers doing it in the right order.
If the phone will not boot far enough to erase
A device stuck at the Apple logo or in a boot loop cannot be erased from Settings. Recovery mode and a restore through a computer is the route — it erases and reinstalls the operating system in one operation.
Our recovery mode guide covers it, and our IPSW guide covers restoring the system itself.
Afterwards
The iPhone restarts to Hello and behaves as new. From there you can set it up fresh, restore from a backup, or hand it on. Restoring is only offered during this setup flow, which is why an in-use phone has to be erased before a backup can be restored.
Our restore guide covers what comes back and the version rule that catches people out.
Frequently Asked Questions
How do I factory reset an iPhone?
Settings → General → Transfer or Reset iPhone → Erase All Content and Settings, then enter your passcode and Apple Account password.
What is the difference between Reset All Settings and Erase All Content?
Reset All Settings keeps your apps and data and returns preferences to defaults. Erase All Content removes everything.
Why does it ask for my Apple Account password?
To turn off Activation Lock. Without that step the erased iPhone stays locked to your account and cannot be set up by anyone else.
Can I undo a factory reset?
No. The only way back is restoring a backup made beforehand, which is why checking the backup date first matters.