Time Machine is built into every Mac and, once configured, requires almost no attention. But “almost no attention” is only true if you set it up correctly from the start. A few choices at setup time determine how reliable your backups actually are when you need them.
What you need
An external drive with at least twice the capacity of your Mac internal storage. More is better: Time Machine keeps older backups and gradually fills the drive, deleting the oldest backups as it runs out of space. A 2 TB drive for a 512 GB Mac is a comfortable starting point.
The drive should be formatted as APFS or Mac OS Extended (Journaled). If you are buying a new drive, it likely comes formatted for Windows (exFAT or NTFS) — you will need to reformat it. Disk Utility can do this.
Format the drive (if needed)
- Connect the drive and open Disk Utility (search for it with Spotlight).
- Select the drive in the sidebar — the top-level device, not a volume underneath it.
- Click Erase.
- Name it something clear (e.g., “Mac Backup”), choose APFS for modern Macs, and click Erase.
This will delete everything on the drive, so make sure it is empty first.
Enable Time Machine
Go to System Settings > General > Time Machine. Click Add Backup Disk, select your drive, and click Set Up Disk.
Time Machine will ask if you want to encrypt the backup. This is worth doing, especially for laptops. Choose a strong password and store it somewhere safe (your password manager is ideal). If you lose the encryption password, the backup is unreadable.
Run the first backup
Time Machine starts automatically and runs hourly when the backup drive is connected. The first backup can take several hours depending on how much data you have. You can use the Mac normally while it runs.
To start a manual backup, click the Time Machine icon in the menu bar and choose Back Up Now.
What gets backed up
Everything in your home folder, system files, and applications. Time Machine does not back up things you can easily re-download: the Mac App Store cache, system logs, and similar files are excluded by default.
If you have external drives you want to include, go to System Settings > General > Time Machine > Options and add them to the backup explicitly.
Exclude items to speed things up
In the same Options panel, you can exclude folders you do not need backed up: large virtual machines, local developer build folders (~/Library/Developer/Xcode/DerivedData), and any other folders with files you can regenerate. Excluding them reduces backup time and conserves drive space.
Restoring from a backup
There are two ways to restore. For individual files or folders: connect the backup drive, open a Finder window to the location you want to restore, then open Time Machine from the menu bar and use the timeline on the right to go back to a previous date. Click Restore to bring back that version.
For a full system restore: restart and hold Command + R to boot into Recovery Mode. Choose Restore from Time Machine Backup and follow the steps.
The single most important habit
Plug the drive in at least once a week. Time Machine only backs up when the drive is connected. An excellent backup drive that you leave in a drawer is not a backup — it is a false sense of security. Keep it on or near your desk and connect it regularly.