Use an old iMac as a monitor: what works for your model
Yes, you can use an old iMac as a monitor for another computer, but what works depends on the year your iMac was made. Apple's Target Display Mode ended with the 2014 models, so every iMac since then needs either an app or a hardware conversion.
In short: a 27-inch iMac from 2017, 2019 or 2020, or an iMac Pro, becomes a full 5K monitor for your Mac with one cable and DisplayBridge, the app I develop. For the 5K iMacs from 2014 and 2015, a conversion kit works today, and DisplayBridge support is coming soon. The 21.5-inch and 24-inch iMacs haven't been tested with DisplayBridge yet.
Step 1: find out which iMac you have
Click the Apple menu in the top-left corner of the screen and choose About This Mac. The window shows the model and the year, for example "iMac (Retina 5K, 27-inch, 2017)". That name is all you need for the table below. If your iMac doesn't start anymore, Apple's support page Identify your iMac model explains how to find it from the serial number.
What works for each iMac
| iMac | What works | What you need |
|---|---|---|
| 27-inch 5K, 2017, 2019 or 2020, and the iMac Pro | DisplayBridge: the iMac becomes a full 5K monitor at 60 Hz for another Mac, with sound. The 2019 and 2020 models and the iMac Pro can also receive AirPlay (wireless, compressed) | A Thunderbolt cable or a 40 Gbit/s USB-C cable, macOS 13 Ventura or later on both Macs, and $29 once after a free 7-day trial |
| 27-inch 5K, Late 2014, Mid 2015 and Late 2015 | A hardware conversion kit today. DisplayBridge support is coming soon | A driver board kit and tools, about $175–205, and more than two hours of work |
| 21.5-inch, 2017 and 2019 | DisplayBridge should work, but hasn't been tested yet. The 2019 model can also receive AirPlay | The same as the 27-inch models: they have Thunderbolt 3 and run macOS 13 |
| 24-inch with Apple silicon, 2021 and later | DisplayBridge hasn't been tested yet. AirPlay to Mac works (wireless, compressed) | For AirPlay: macOS Monterey or later on both Macs |
Each of the supported models has its own short page with its facts and current used prices: the iMac 2017, the iMac 2019, the iMac 2020 and the iMac Pro.
iMacs from mid-2014 and earlier are a different story: many of them had Apple's Target Display Mode, with strict limits. My Target Display Mode guide explains which ones and why the 5K iMacs never had it.
iMacs from 2017 to 2020 and the iMac Pro: one cable and DisplayBridge
These are the iMacs that work best as a monitor, because they have Thunderbolt 3 ports and run macOS 13 Ventura. With DisplayBridge, you install the same app on the iMac and on the Mac you work on, connect the two with one cable, and click Connect. A few seconds later, the iMac appears in System Settings as a second display of your Mac, and you use it like any external monitor: move windows to it, place it to the left or right, or make it your main screen.
The picture is sent uncompressed, at the full 5K resolution and 60 Hz, and the Mac's sound plays through the iMac's speakers over the same cable. The delay is roughly 10 milliseconds longer than with a directly connected monitor, which is unnoticeable in everyday use. What you need:
- A second Mac with Thunderbolt 3 or 4 on macOS 13 Ventura or later, for example a MacBook Pro from 2017 on, a MacBook Air from 2018 on, a Mac mini or a Mac Studio.
- A Thunderbolt cable or a 40 Gbit/s USB-C cable (USB4). A normal USB-C charging cable looks the same but does not work; look for the lightning symbol on the plug or "40 Gb/s" on the packaging. Good ones start at about $10.
- One license for the Mac you work on: $29, paid once, after a free 7-day trial. The iMac never needs a license.
One thing to know: the iMac stays a full Mac. It has to be switched on and logged in, because it runs DisplayBridge as the receiving side, and when you disconnect, it is your computer again. The setup guide walks through the first connection step by step.
The 2019 and 2020 models and the iMac Pro can also receive AirPlay to Mac, which is free and wireless, but compresses the picture and doesn't run the panel at its native 5K. My Target Display Mode guide compares AirPlay and DisplayBridge side by side.
5K iMacs from 2014 and 2015: a conversion kit, or wait for DisplayBridge
The first 5K iMacs from Late 2014, Mid 2015 and Late 2015 have the same beautiful 27-inch 5K panel, but only Thunderbolt 2 ports. DisplayBridge doesn't support them yet; support is coming soon.
If you don't want to wait, a hardware conversion kit works today. You open the iMac, remove its logic board and install a driver board that gives the panel its own DisplayPort, USB-C and HDMI inputs. Then any computer, including a Windows PC or a game console, can use it as a monitor. The parts and tools cost about $175 to $205, the work takes more than two hours, the glass panel can crack while you lift it out, and the iMac can never be used as a computer again. I've done this conversion myself; my conversion kit guide covers the parts, the steps and the risks.
21.5-inch and 24-inch iMacs: not tested yet
The 21.5-inch iMacs from 2017 and 2019 have Thunderbolt 3 and run macOS 13, so they meet DisplayBridge's requirements, and they should work as a display. I haven't tested them yet, so I'm not promising it.
The 24-inch iMacs with Apple silicon, from 2021 on, also have Thunderbolt and run current macOS, but I haven't tested DisplayBridge with them either. What works with them today is AirPlay to Mac: wireless and free, with a compressed picture.
If you own one of these iMacs, downloading the free 7-day trial is the easiest way to find out: it costs nothing, and you'll know within a few minutes whether it works with your Macs.
Is it worth using an old iMac as a monitor?
For the 27-inch 5K models, I think it clearly is. Their panel shows 5120 × 2880 pixels, and a new 5K monitor still costs several hundred dollars, Apple's own considerably more. Used 5K iMacs, on the other hand, often sell for a few hundred dollars; I bought my 2017 5K iMac used for less than 200 Swiss francs. With DisplayBridge, that iMac becomes a full 5K monitor for $29, without opening it, and it stays a working Mac you can still sell later.
The trade-offs are honest ones: an iMac takes up more room than a monitor, it has to be switched on and logged in to work as a display, and with DisplayBridge it only works with a Mac on the other end. If you want to connect a Windows PC or a game console, the conversion kit is the way to go.
Questions about this
Can you use an old iMac as a monitor?
Yes, but the way depends on the model. A 27-inch iMac from 2017, 2019 or 2020, or an iMac Pro, works as a full 5K monitor for another Mac with DisplayBridge and one Thunderbolt cable. A 5K iMac from 2014 or 2015 needs a hardware conversion kit for now; DisplayBridge support for these models is coming soon. Many iMacs from 2009 to mid-2014 had Apple's Target Display Mode.
Which MacBooks can use an old iMac as their monitor?
With DisplayBridge, any MacBook with Thunderbolt 3 that runs macOS 13 Ventura or later: a MacBook Pro from 2017 or a MacBook Air from 2018 onwards. The iMac has to be a 27-inch model from 2017 or later or an iMac Pro, and the two are connected with one Thunderbolt or 40 Gbit/s USB-C cable.
What if the other computer is a Windows PC?
Then software like DisplayBridge can't help, because it only connects two Macs. The way to connect a Windows PC or a game console to a 2014 to 2020 iMac by cable is a hardware conversion kit, which turns the iMac into a monitor with DisplayPort, USB-C and HDMI inputs, but ends its life as a computer.
Does DisplayBridge work with the 24-inch iMac?
It hasn't been tested yet. The 24-inch iMacs with Apple silicon have Thunderbolt and run current macOS, so they meet the basic requirements, but I don't promise support until I've tested them. The free 7-day trial lets you check it on your own iMac without paying.
What can I do with a 2015 5K iMac?
Today, a hardware conversion kit turns it into a 5K monitor for any computer, at about 175 to 205 dollars in parts and tools and more than two hours of work. DisplayBridge support for the 2014 and 2015 5K iMacs is coming soon, which will make it possible without opening the iMac.
How do I find out which iMac I have?
Click the Apple menu in the top-left corner of the screen and choose About This Mac. The window shows the model and year, for example iMac (Retina 5K, 27-inch, 2017). If the iMac doesn't start, Apple's support page Identify your iMac model explains how to find it from the serial number.