How to use an iMac as an external monitor for a MacBook

If you have an older iMac sitting around then you may have wondered if it can be used as an external display. There used to be a feature on iMacs called “Target Display Mode”, and while it unfortunately doesn’t exist on newer iMacs, some models made in 2014 or prior do have it. This effectively lets the iMac act as a monitor for another computer. While it is possible to use Target Display Mode with the source as a Windows computer, in this article we will be focusing on how to connect a MacBook specifically. So read on to find out how to setup your iMac as an external display for your MacBook step-by-step!

Determine if your iMac supports Target Display Mode

The first step is to determine if your iMac supports Target Display Mode in the first place. Any iMac since 2014 will not support it, according to Apple, as the resolution of the Retina displays are too high to be run by one Thunderbolt or Mini-DP cable.

Is the iMac a compatible model?

To find your iMac’s model go to the Apple Menu > About This Mac. If it is any of the following models then it will support Target Display Mode:

• 27″ iMac late 2009 & mid 2010
• 21″ & 27″ iMac mid 2011 to mid 2014

Does the iMac run a compatible version of macOS?

You will also need to make sure that the iMac is running macOS High Sierra 10.13 or earlier. Newer versions of macOS do not support Target Display Mode, even if the iMac is one of the compatible models.

Determine which video output your MacBook has

The next step is to determine what sort of video output your MacBook has, as this will tell you which video cable you’ll need to connect the iMac, or if it’s even possible to connect it at all. Unless the MacBook is super old, it will be one of these four ports:

Mini-Display port

This port is found on older MacBooks. You should be able to see the Mini-Display port logo next to the port, which features on the following MacBooks:

• MacBook Air 2008-2010
• MacBook Pro 2008-2010

Thunderbolt 1/2 port

Thunderbolt ports look the same as the Mini-Display port, however they will feature a Thunderbolt logo next to the port instead. They come on the following MacBooks:

• MacBook Air 2011-2017
• MacBook Pro 2011-2015

USB-C (Thunderbolt 3) port

A USB-C port with Thunderbolt 3 capability is included on the following MacBooks:

• MacBook Air 2018 or later
• MacBook Pro 2016 or later

USB-C (Display-port only, no Thunderbolt) port

The 12″ MacBook (2015-2018) will have a USB-C port that supports only Mini-DP, not Thunderbolt.

Find a video cable to connect your MacBook to the iMac

Now you’ll need to find a video cable (and possibly adapter) to connect the MacBook and iMac. Which video cable will be needed depends on the MacBook being used, as well as the iMac model. Not all combinations of MacBook and iMac are compatible either, so take a look at the table below to find out which cable/adapter you’ll need based on the Macs you are trying to connect together:

Purchase the correct cable via Amazon

Below are Amazon listings for the different cables that were specified in the table above, so you can purchase the appropriate one to connect your MacBook and iMac if you don’t already have it:

Mini-DP to Mini-DP cable$8.49USDBUY NOW VIA AMAZON
USB-C to Thunderbolt 2 adapter$49.99USDBUY NOW VIA AMAZON
Unidirectional USB-C to Mini-DP cable$17.99USDBUY NOW VIA AMAZON
Thunderbolt 2 cable$44.99USDBUY NOW VIA AMAZON

Put the iMac into Target Display Mode

Once you have connected your MacBook and iMac using the appropriate cable, all you should need to do is enter Target Display Mode on the iMac. This can be done by pressing Command-F2 on the iMac’s keyboard. Press the same combination to go back to normal, or simply unplug the video cable.

What if Target Display Mode doesn’t work?

If after pressing Command-F2 the iMac doesn’t start displaying your MacBook’s screen, review the below troubleshooting steps:

• Make sure the MacBook is logged into an account, not sitting on the login screen.
•  In System Preferences > Keyboard make sure the box is ticked to “Use F1, F2 etc keys as standard function keys”.
• Try starting both the MacBook and iMac in Safe Mode to see if third party apps are interfering with Target Display Mode. To start in safe mode shut the Mac down, then hold the Shift key while starting back up until the Apple logo appears.
• Try using an original Apple keyboard (such as the one that came with the iMac) if possible, as some third party keyboards will not work correctly to activate Target Display Mode.

Additional Resources

Below are resources this article sourced information from, or which you may find helpful:

• Use your iMac as a Display (Apple)
• Identify your iMac Model (Apple)
• Identify the ports on your Mac (Apple)
• The Ins and Outs of your iMac’s Target Display Mode (TechJunkie)

Share your experience!

Were you unable to get Target Display Mode working? Do you have some tips or other information not mentioned in this article? Then please share it in the comments section below to assist other people, or so other people can assist you.