What you need to know before you start

You can use an iMac as a monitor for another Mac, but not for Windows PCs, iPad, or iPhone — and not for all iMacs. The feature is called Target Display Mode, and it only works on iMacs made between 2006 and 2014. If your iMac is newer than 2014, this route is closed to you.

Target Display Mode turns your iMac into a passive display that receives video from another Mac over Thunderbolt or Mini DisplayPort. The iMac's own processor shuts down; it becomes just a screen. You control everything from the other Mac, which must also be a Mac — a MacBook, Mac mini, or another iMac.

If your iMac is 2014 or newer, or if you need to connect a Windows machine or iPad, you will need a different approach: either a third-party app like Luna Display or Duet, or an external monitor plugged into your Mac's video port.

Key Takeaways

  • Target Display Mode works only on iMacs from 2006 to 2014 with Thunderbolt or Mini DisplayPort, and only when connected to another Mac.
  • You connect the two Macs with a Thunderbolt or Mini DisplayPort cable, then hold Command+F2 on the iMac's keyboard to activate the mode.
  • Once active, the iMac's screen displays whatever the other Mac is showing, and you control everything from the other Mac's keyboard and trackpad.
  • iMacs made after 2014 do not support Target Display Mode, and Apple has not released an official replacement feature.
  • Third-party apps like Luna Display and Duet can turn newer iMacs into secondary displays, but they require a small hardware adapter or software subscription.

Checking whether your iMac supports Target Display Mode

Open the Apple menu on your iMac and select About This Mac. Look at the year listed next to the model name — if it says 2014 or earlier, your iMac may support the feature. If it says 2015 or later, Target Display Mode is not available, and you will need to use a third-party solution instead.

You also need to confirm your iMac has the right video port. iMacs from 2006 to 2013 have Mini DisplayPort. iMacs from 2014 have Thunderbolt. Both ports look similar — a small rectangular connector with a lightning bolt symbol (Thunderbolt) or no symbol (Mini DisplayPort). If your iMac has USB-C ports instead, it is too new and does not support Target Display Mode.

The other Mac you want to connect must also have Thunderbolt or Mini DisplayPort and must be running macOS 10.4 or later. Most Macs from 2008 onward meet this requirement, but check the specs of your specific model if you are unsure.

How to set up Target Display Mode

Shut down the iMac completely. Do not put it to sleep — turn it all the way off.

Connect the two Macs with a Thunderbolt or Mini DisplayPort cable. Use the correct cable for your ports: Thunderbolt to Thunderbolt, Mini DisplayPort to Mini DisplayPort, or a Thunderbolt cable to a Mini DisplayPort adapter if the ports do not match. The cable must be a video cable, not a charging cable.

Turn the iMac back on. While it is starting up, hold down Command+F2 on the iMac's keyboard. Keep holding until you see the video input from the other Mac appear on the iMac's screen. This usually takes 10 to 15 seconds. Release the keys once the image appears.

The iMac is now in Target Display Mode. Its screen will show whatever is on the other Mac. Use the other Mac's keyboard, trackpad, and mouse to control everything — the iMac's keyboard and trackpad will not work for input while in this mode.

Exiting Target Display Mode

To exit Target Display Mode, hold Command+F2 again on the iMac's keyboard. The iMac will return to its normal startup sequence and boot into its own operating system.

Alternatively, shut down the other Mac or disconnect the cable. The iMac will exit the mode automatically and return to normal operation.

Using a third-party app if your iMac is too new

If your iMac is from 2015 or later, Target Display Mode is not an option. Luna Display and Duet are the most common third-party solutions. Both let you use your iMac as a secondary display for a Mac, iPad, or Windows PC, though the setup and cost differ.

Luna Display requires a small hardware adapter that plugs into your iMac's Thunderbolt or USB-C port. The adapter costs around $80 and works with Macs, iPads, and iPhones. Duet also offers a hardware version, but it primarily works through software — you install an app on both devices and connect over Wi-Fi or USB. Duet's software subscription costs around $20 per year.

Both apps introduce a slight delay (usually under 100 milliseconds) compared to Target Display Mode, which has no delay. For everyday work like email or web browsing, the delay is not noticeable. For video editing or gaming, you may notice it.

Troubleshooting common problems

If the iMac does not enter Target Display Mode after holding Command+F2, try these steps: First, make sure both Macs are fully powered on and the cable is firmly seated in both ports. Second, try the keyboard shortcut again — sometimes it takes a few attempts. Third, restart both Macs and try again.

If the iMac screen stays black or shows a "no signal" message, the cable may be damaged or the port may not be working. Try a different Thunderbolt or Mini DisplayPort cable if you have one. If that does not work, the video port on one of the Macs may need repair.

If you see the video from the other Mac but the iMac's keyboard and trackpad do not work, that is normal — they are disabled in Target Display Mode. Use the other Mac's keyboard and trackpad to control everything.

Frequently Asked Questions

Can I use Target Display Mode with a Windows PC?

No. Target Display Mode only works between two Macs. If you want to use an iMac as a display for a Windows computer, you will need a third-party app like Luna Display, which supports Windows machines.

Will my iMac overheat if I leave it in Target Display Mode for hours?

No. In Target Display Mode, the iMac's processor is off and only the display is active, so it generates very little heat. You can safely leave it running this way for extended periods.

Can I use Target Display Mode wirelessly?

No. Target Display Mode requires a physical Thunderbolt or Mini DisplayPort cable connection. If you want wireless display sharing, use AirPlay (available on newer Macs) or a third-party app like Duet.

What happens to the iMac's apps and files when it is in Target Display Mode?

They are not accessible. The iMac's operating system is not running — only the display hardware is active. All your files and apps remain on the iMac's drive, but you cannot use them until you exit Target Display Mode and the iMac boots normally.

Is there an official Apple replacement for Target Display Mode on newer iMacs?

No. Apple removed Target Display Mode starting with the 2015 iMac and has not released an official replacement. Third-party apps like Luna Display and Duet are the main alternatives for newer models.