Does Time Machine back up while your Mac sleeps?

Does Time Machine run while the Mac sleeps?

Only through Power Nap. Apple’s Power Nap page says Power Nap “lets some Mac computers stay up to date even while they’re sleeping”. On a power adapter, that includes “performing Time Machine backups”.

Easiest way: Napless. It can stay awake while Time Machine backs up, then let the Mac sleep when the backup is done. It does not wake a sleeping Mac to start a backup. Try Napless free for 7 days.

Without Power Nap, backups happen while the Mac is awake. In an Apple Community thread about a MacBook Air (2022), a Community Specialist answered on Aug 27, 2022 that “Time Machine will not automatically back up while your Mac is asleep” because that model lacks Power Nap. Another said that as long as the computer is powered on and not asleep, it should complete the backup.

That schedule only runs while the Mac is awake. Apple’s Time Machine article says it “automatically makes hourly backups for the past 24 hours, daily backups for the past month, and weekly backups for all previous months”. You can change this with the “Back up frequency” menu in Time Machine settings.

Apple also notes that “The first backup might take longer than you expect”, and a long first backup is the one sleep is most likely to cut off.

What does Power Nap do for backups?

Power Nap does Time Machine backups only on a power adapter; on battery it just refreshes Mail, Calendar and iCloud. Apple’s Power Nap settings page splits it this way:

Power source	What Power Nap does while the Mac sleeps
Battery	Checks for new messages in Mail, updates events in Calendar, updates other iCloud events
Power adapter	All of the above, plus downloading software updates and performing Time Machine backups

Apple’s Power Nap page says the feature is available on Mac computers with flash memory. The settings page adds that, where it is supported, Power Nap is on by default when the Mac is plugged into a power adapter.

Because Power Nap does work while the Mac sleeps, check it first when you look into why a Mac wakes from sleep by itself.

Which Macs show the Power Nap option?

Laptops show it in System Settings > Battery > Options, as an “Enable Power Nap” menu. Desktops show it in System Settings > Energy, but Apple’s settings page says the desktop option is “only available on Intel-based Mac computers”.

Mac	Where the setting is	Notes
Mac laptop	System Settings > Battery > Options > Enable Power Nap	Backups only on power adapter
Intel desktop (iMac, Mac mini, Mac Pro)	System Settings > Energy > Enable Power Nap	Backups only on power, which a desktop always is
Apple silicon desktop	No Power Nap setting in Energy	Keep the Mac awake for backups

Some laptops lack it too. In the Apple Community thread above, specialists said the MacBook Air (2022) does not support Power Nap.

Terminal tells you whether your own Mac has it:

pmset -g cap
pmset -g

man pmset says -g cap “displays which power management features the machine supports”, and powernap enables Power Nap “on supported machines”. If powernap appears in the pmset -g cap list, the Mac supports it. pmset -g then shows powernap 1 if it is on, or powernap 0 if it is off.

On a MacBook Pro with Apple silicon running macOS 27.2, pmset -g cap listed powernap under “Capabilities for AC Power”, and pmset -g showed powernap 1.

How do you keep the Mac awake until a backup finishes?

Start the backup from Terminal under caffeinate, so the hold ends when the backup does:

caffeinate -i tmutil startbackup --block

What each part does:

man tmutil says startbackup begins “a backup if one is not already running”, and --block makes it “Wait (block) until the backup is finished before exiting”.
man caffeinate says -i prevents idle sleep, and that with a command the hold lasts “for the duration of the utility’s execution”.

Run it before a backup has started. To see whether one is already running, use tmutil status, which prints Running = 1 during a backup and Running = 0 otherwise.

On a laptop, plug in first and leave the lid open. Apple lists closing the display as a way to put a Mac laptop to sleep. man caffeinate adds that -s, the stronger system-sleep hold, “is valid only when system is running on AC power”. The caffeinate command guide has the other flags.

Without Terminal:

Click Time Machine in the menu bar and choose Back Up Now, as Apple’s backup controls page describes.
Hold the Mac awake for the length of the backup. On a laptop on power, turn on Battery > Options > “Prevent automatic sleeping on power adapter when the display is off”. On a desktop, turn on Energy > “Prevent automatic sleeping when the display is off”. Both are on Apple’s sleep and wake settings page.
Turn the setting back off afterward if you want the Mac to sleep normally. Apple notes that preventing sleep “may increase power consumption”.

Napless timers also work here during the 7-day trial, and on a Mac that installed Napless before 1.5: choose Keep Awake For with a duration longer than the backup, or Keep Awake Until a time. After the trial, keeping the Mac awake needs Napless Pro. How to keep a Mac awake compares the options.

How do you check a backup is holding sleep?

Run tmutil status to confirm a backup is running, then pmset -g assertions to see whether anything is holding the Mac awake while it runs. If no process holds sleep, the backup is not protected.

tmutil status
pmset -g assertions
pmset -g log | grep backupd

Look for a Time Machine process such as backupd or backupd-helper in the “Listed by owning process” section. On our test Mac, which had no backup disk set up, the power log still showed backupd-helper creating a short PreventUserIdleSystemSleep assertion named “Mutexed Backup Block” with a duration of 00:00:00.

We could not run a full backup on that Mac, so this guide does not claim which assertion a long backup holds, or whether it holds one the whole time. Check during a real backup. If no Time Machine process appears, or sleep in pmset -g is not marked “sleep prevented by”, add your own hold as described above.

The guide to reading pmset -g assertions explains what each assertion type does.

What does the Napless Time Machine trigger do?

Napless Pro can keep the Mac awake for as long as Time Machine is backing up, then let it sleep. It is the “While Time Machine is backing up” checkbox in Settings > Triggers > Conditions. Napless Help says it is off by default, and that the “Turn on automatic Keep Awake” switch must also be on.

While a backup runs, the Napless menu gives the reason as “Time Machine is backing up”, so you can see the hold and its cause without opening Terminal.

Napless Help describes the trigger as keeping the Mac awake while a backup runs. It does not describe waking a sleeping Mac, so a backup that would start during sleep still needs Power Nap.

Organizations can turn the trigger off with the managed key NAPDisableTimeMachineTrigger (Napless for IT).

During the trial, and on a Mac that installed Napless before 1.5, timers cover a backup you start yourself. After the trial, keeping the Mac awake needs Napless Pro. Pricing and the Pro feature list are on the Napless Pro page. To hold sleep for the backup, Try Napless free for 7 days.

Questions

Does Time Machine back up when a MacBook is asleep?

Only if the MacBook supports Power Nap and is connected to a power adapter. Apple lists Time Machine backups among the jobs Power Nap does on power, not on battery.

Does closing the lid stop a Time Machine backup?

Closing the lid puts a Mac laptop to sleep, per Apple. Unless Power Nap backs it up on power, the backup has to finish while the Mac is awake.

How do I keep my Mac awake until Time Machine finishes?

Run caffeinate -i tmutil startbackup --block in Terminal. tmutil waits until the backup is finished, and caffeinate holds idle sleep for as long as tmutil runs.

Does Napless keep a Mac awake during Time Machine backups?

Napless Pro has a While Time Machine is backing up trigger. It is off by default and needs automatic Keep Awake turned on. Timers are included in the trial; after it, Napless Pro. Installed before 1.5? You keep those free features.