Back up your Mac to an external drive with Time Machine, set up once and forgotten

Time Machine is built into every Mac and backs it up every hour once set up. The setup takes five minutes; the first backup takes a few hours.

1. Pick a drive

• Size: two to three times the space used on your Mac. Check with df -h /System/Volumes/Data.
• Type: a hard drive is fine and cheapest. See external SSD or hard drive.
• Use it only for backups, or give backups their own volume. See using part of a Time Machine drive.

2. Set it up

1. Plug the drive in.
2. Open System Settings, General, Time Machine and click Add Backup Disk.
3. Choose the drive and tick Encrypt backup. Set a password and save it somewhere safe.
4. Confirm. If the drive is not already suitable, macOS erases and formats it.

3. The first backup

The first backup copies everything and can take several hours. Keep the Mac plugged in and awake. After that, backups are hourly and only copy what changed, so they are quick.

4. Leave out what does not need backing up

In the Time Machine settings, click Options and add folders to exclude. Good candidates:

• Downloads, if you only keep installers there.
• Virtual machine disks and Docker data, which change constantly and are large.
• Developer caches that rebuild, such as DerivedData and node_modules.

5. Check it works

tmutil latestbackup
tmutil listbackups | tail -3

Once in a while, open Time Machine and restore a test file. A backup you have never restored from is a guess.

If the backup drive fills, see Time Machine backup drive full. Comparing with a bootable clone: Carbon Copy Cloner versus Time Machine.

Related: Time Machine must create a new backup.