macOS: How to Use Your Old iMac as an External Monitor

Mahit Huigol

4 minute read
| How-To
  • Learn how to repurpose your old iMac as an external monitor.
  • Turn your old iMac into a secondary wireless display with AirPlay
  • Easily control brightness and volume of the external iMac from the primary device.
Apple iMac 2017

Apple products have a reputation for lasting longer than others. No matter what, eventually, you will have to upgrade to a newer machine. But what if your iMac is still working? We will explain how to repurpose your old iMac as an external monitor. All you need is an old iMac that supports Target Display Mode. Apple added the feature on iMac’s sold after 2009.

The caveat is that Apple retired the Target Display Mode with Retina Displays. However, there is a nifty workout just for this. We have listed the basic system requirements and multiple ways to use the old iMac as an external monitor.

System Requirements for Using Your iMac as a Secondary Display

If you are looking to use your iMac as a secondary display, you will need a few things to prepare your entire setup. What are those things?

The source Mac must be running macOS Catalina (10.15) or earlier.

  • The 27-inch iMacs, which are Display mode-compatible, usually feature a Thunderbolt port or a bi-directional Mini Display port. So depending on which port is present in your iMac, you will need the Thunderbolt or the Mini DisplayPort cable to facilitate the connection between the two Macs.
  • The macOS on the iMac should be High Sierra (10.13.6) or earlier.
  • The source Mac must be running macOS Catalina (10.15) or earlier.

List of Compatible Macs

The iMac models released over the years 2011 and 2014 are all compatible with functioning as a secondary display. 

  • 2009-2010 27-inch Mac -that has a Mini DisplayPort
  • 2011-2014 iMac – that has a Thunderbolt port. 

Set up an Old iMac as an External Monitor Using Target Display Mode

The Target Display Mode feature (TDM) allows specific iMac models that have Thunderbolt or Mini DisplayPort interface to function as an external secondary monitor for another Mac. The latter Mac models do not have this feature because the power and port sustainability was becoming an issue with an increase in display quality.

Steps to Set up Target Display Mode

Let me show you how to enable Target Display Mode and use your iMac as a secondary display. 

Time needed: 3 minutes

Follow the steps below to connect the two Macs and setup Target Display Mode.

  1. Turn on both the display iMac and the source Mac. 

  2. Connect the two Macs with either Thunderbolt or a Mini DisplayPort cable.

  3. Usually, the connection happens automatically. If it doesn’t, then press Command + F2 to manually enter into TDM. You will then see the screen contents of your Mac being displayed on the iMac. 

  4. When you are done with the system, you can press Command + F2 to manually exit Target Display Mode or you can just sever the cable connections between the two Macs to turn it off. 

How To Control Brightness and Sound on the Display Mac?

There are two easy ways in which you can control the brightness and sound of your display Mac. 

1. Move your mouse cursor on the screen of the display iMac and then press the keyboard buttons for adjusting brightness and sound. 

2. Use the sliders on the menu bar item to control the sound and brightness of the second display Mac.

Fix Target Display Mode is Not working

If your Target Display Mode is not functioning properly, there is no need to panic. Here are some solutions which you can try out to fix the issue. 

1. Instead of Command + F2, use Command + Fn + F2. This solution might help for some specific keyboard types. 

2. Check and ensure that the Thunderbolt or the Mini DisplayPort cables are connected properly. 

3. If you have already logged into the iMac that you intend to use as a secondary display, log out and come back to the login screen. 

4. Booting up the display iMac from a Windows volume also might cause the issue. In that case, you will have to restart it from a normal Mac startup drive. 

5. Some third-party keyboards create an issue while sending the Command + F2 prompt. In that case, it is advised to use a different keyboard or the keyboard that came with the Mac. 

How To Use iMac as an External Monitor With Airplay?

The AirPlay feature allows you to receive audio, videos, and other content from nearby Apple devices (iPhone, iPad, or Mac). AirPlay is supported on Macs which run macOS 12 or later. If you wish to learn about the system requirements for the continuity of AirPlay across devices, you can go through Apple’s Support Guide.

Note: If your Mac is enrolled in an MDM (Mobile Device Management) system, the AirPlay Receiver may be unavailable on your device.

Set Up iMac To Become an AirPlay Receiver

Here is how you can set up your iMac as an AirPlay receiver. 

1. Go to the Apple menu on your Mac. 

2. Open System Settings and go to General in the sidebar. 

3. Click on Airdrop & Handoff on the right side to turn it on. 

You will find three options –

  • Current user: Only the devices in which you are signed in with your own Apple ID can be used to stream content on this Mac. 
  • Anyone on the same network: Any nearby Apple device which has AirPlay enabled can stream content to this Mac. 
  • Everyone: Any nearby iPhone, iPad, or Mac can use this monitor to stream content. 

4. If you wish to keep your iMac password protected, turn on Require Password and enter the password in the text field. Sometimes AirPlay might become sluggish. In such a scenario here’s how you can fix lagging AirPlay.

When Should You Use iMac as a Monitor?

If you need a second display monitor temporarily or on an urgent basis, using your iMac as a second display monitor is a great option. But if you are looking for a more permanent solution then I will advise getting a separate monitor for your requirements. 

If you continue using an iMac as a secondary monitor for prolonged period, you will be wasting both power and the computing abilities of the iMac. 

Old iMac Gets a New Lease of Life

Old iMac monitors are decent and good for a non-demanding workflow. The iMac will serve well as an external monitor instead of scrapping it as e-waste. Do note that we don’t recommend using newer iMacs as external monitors. Since it is better used as a standalone computer.

28 thoughts on “macOS: How to Use Your Old iMac as an External Monitor”

  • First off – THANK YOU – this is the best article about this issue, both concise, descriptive, and well-organized. Important things first, then all the details etc.

    HOWEVER – I think you missed several important points – and for me – THE point. iMac 27″ provides one of the best screens EVER with a resolution so high, that has real impact on readability for people with deteriorating eye-sight (I’m over 57, and it becomes really straining to read off other screens). In addition – There are almost NO OPTIONS for buying competing monitors with that kind of display resolution and clarity!!! My old iMac (alas non-eligible, because it’s mid 2015) looks a zillion times better than any “Dell” or “Phillips” or actually any other display I could buy today – 2023. It’s horrible – my only option is the outrageously priced Apple Studio-display (min $1600) or the $5000 Pro Display XDR!

    All I want is to move to new computer, but still have my old, existing, beautiful display! isn’t that a good motivation? It’s not about using old hardware. It’s about using superior hardware, that was already paid for, and without any reasonable alternative!!

    Now the restriction of OS versions (10.13 on the receiving old iMac, and no more than 10.15 on the sending Mac) renders this intention useless. I want a new M1 or M2 Mac-mini…

    So my last question, about Airplay. Is Airplay a viable option for using an old iMac as a monitor? Is the quality supported in airPlay sufficient? except for “by air – WiFi” can AirPlay also use another – faster – connection?

    And also, you did NOT specify a list of AirPlay compatible (old) iMacs, and whatever limitations they have (in terms of MacOS, memory, speed etc.)

    Last – we know Apple won’t support TDM feature on MaccOS higher than 10.13 (long time dead) an I wonder… can this limitation be broken? have anyone tried? Also – what if I’m trying to do that on a Virtual MacOS 10.13 running inside a VM ? Any idea?
    Would love to hear more details.

  • Hello! I have a 2020 Macbook Air running on Ventura 13.5.1 and the Intel Chip. I’m trying to extend it to a 27 inch, late 2013 iMac running on Catalina. Is there a way I can connect these two without buying a cable? I was following the instructions, but system settings only has handoff, not handoff and airplay. If not, what kind of cable would work for this? Thanks

  • I have a MacBook Pro (15-inch, 2019) running macos monterery 12.1 and iMac (27-inch, Mid 2010) macOS High Sierra 10.13.6 and the apple thunderbolt cable and usbc adapter I bought does not command F2 into TDM. What am I doing wrong???

  • Hi I did the following but my imac is dimmed. I can see the windows but the monitor is so dark. Before I can restart both and it works but now it doesn’t seem to work. Have you had this problem? Thanks

    1. Hello Raquel and sorry for the late response. From what we’ve found, it seems that making the external monitor the primary display will allow you to adjust the brightness. The white bar at the top of your primary display may be moved to the secondary monitor by dragging it after you go to System Preferences > Displays > Arrangement tab. The brightness of the external monitor may then be changed using sliders or the brightness buttons on the keyboard. Drag the white bar back to your main display once you’ve got it how you like it.

  • I have a 2015 Imac that from what I understand can no longer be upgraded. It is very slow and sluggish on startup making it hard for me to continue using it for my work. I’ve cleaned it up as much as possible and use an external drive for just about everything. I have a new mouse and keyboard that I upgraded not long ago, so I hate to buy a whole new Imac. I was thinking of getting the mini and using the Imac as my display for it.
    Would that work? If so, would it be a pain to deal with all day working (such as disconnecting when monitors sleep etc.)

    2. Hi Kelly, you might be able to do that with target display mode if you connect the Mac mini to the iMac with a Thunderbolt cable. The only caveat is that requires macOS High Sierra or earlier; it doesn’t work with macOS Mojave or later. Apple has a guide here.

  • hi. i created an account just in order to leave this comment. sure, appreciate your effort, but please specify in your report that this TDM thing ONLY applies to 27” imacs, as i just recommended my sister based on this article and now she has to send back cables she bought in order to do this as our imac is 24”. i know it’s my fault not having verified straight away the source you’ve indicated. still i think it can be deceptive putting it the way you did, so telling this for possible future misadventurers following me

    1. Hello, and sorry for the delayed reply. You can connect more external monitors by selecting Apple menu from the sidebar > System Settings > Displays. Then, select Add Display and choose your display.

  • I’ve managed to connect my iMac and MacBook pro following your instructions. Thanks! Is it possible to make the MacBook pro the second monitor not the iMac? Doesn’t seem to do anything when I click fn, cmd and F2 on the MacBook pro. When I do it on the iMac it jumps into target display mode. I’m suing thunderbolt to thunderbolt.

    1. Hello Lee, you can go to System Preferences > Displays > Arrangement tab then change the primary and secondary monitors from there, and sorry for the late response.

  • Hello – I’m betting you’ll know the answer to this. We just bought a 2020 Mac Mini, and we want to use our Late 2013 iMac as the monitor. What’s the easiest way to connect the Mac Mini and iMac … can I do it with a single cable and no adapter? Or do I have to buy an adapter AND a cable?
    Thanks so much!
    Bart

  • Looking at adding an extra “extended” monitor to my iMac 27″, would like it to be a monitor that looks like my iMac. I may add another to the other side, go 3-screens.

    1) Does the other iMac have to be operational?

    2) If I add two additional screens to my iMac, how do I connect them, even if they are not Mac products?

    1. I would assume the other iMac has to at least be able to turn on. Monitors can connect to the Mac via the Mini DisplayPort, Thunderbolt, or USB-C. On the monitor itself it will connect through the VGA, HDMI, Thunderbolt, or USB-C. You might have to get an adapter for monitors with VGA or HDMI.

  • Another approach that’s workable is to link the two Macs via an Ethernet cable & use screen sharing. I was recently demonstrating a 2005 G4 PowerBook connected to a video projector. When I finished that, I needed to connect my Thunderbolt 3 MacBook Pro to the projector but didn’t have an adapter with me.
    But I did have an Ethernet adapter & Ethernet cable. I was able to share the MacBook Pro’s screen to the PowerBook & thence to the projector. At the same time, the Ethernet connection was providing internet to the PowerBook from Internet (wi-fi) Sharing via Ethernet on the MacBook Pro.

  • Also wondering if a USB C to Display port adapter cable would work?
    – in the example of a new Macbook Pro and 2013 iMac (Which currently supports target display mode)

    1. Hello Costas and sorry for the delayed response. A DisplayPort output may be connected to a USB-C display using a bi-directional USB-C to DisplayPort connection. Only USB-C output to DisplayPort displays will function with standard USB-C to DisplayPort connections.

  • Thought this would be a good way to use my 2011 iMac screen with a Mac mini (assuming a new one ever appears) but from the Apple support article it seems to imply that the ‘master’ Mac must have a screen of its own so it can log into macOS first. Or is there another way of achieving this?

    1. Hello Colin, and sorry for the delayed reply. You will need to use a different display first, to log into your Mac mini (maybe borrowed from someone else), then enter TDM. This is not an ideal solution, because it will need to be done every time the Mac mini reboots.
      TDM was never really meant to be a full-time substitute for a dedicated display for a Mac. More like a troubleshooting or interim use type of thing.

  • So according to Apple’s support page this only works on iMacs up to 2014. The 5K Retina and newer ones don’t support this. That really sucks. Anyone know why? Is it a hardware issue or software?

    1. I use it on my 27″ 2010. It’s critical to me being able to work from home without rearranging my whole workstation. I simply plug in my work laptop to my iMac and bring my keyboard and mouse USB hub over.

      I’ve been following a discussion about it on MR, where there was a glimmer of hope that it would return, but alas, nothing has come out of it:

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