How to use an old iMac as a second monitor for your MacBook

If you have an older iMac sitting on your desk, especially a 27-inch Retina 5K model, you may have wondered: can I use my iMac as a second monitor for my MacBook? This guide explains what works and how you can turn an older iMac into a true extended display without opening it or modifying its hardware.

At a glance: which iMacs can be used as a monitor

Why can't I simply connect a MacBook to my iMac?

An iMac may have Thunderbolt ports, but that does not automatically mean its built-in display accepts a video signal like a conventional external monitor. Apple solved this on certain older iMacs with a feature called Target Display Mode.

According to Apple's support documentation, Target Display Mode works with iMac models introduced in 2011, 2012, 2013 and Mid 2014, provided the iMac is running macOS High Sierra 10.13.6 or earlier. There is another major restriction: the source Mac must have been introduced in 2019 or earlier and must be running macOS Catalina 10.15.8 or earlier.

So while Target Display Mode still technically exists for compatible legacy hardware, it is generally not a practical solution if you want to connect a modern Apple Silicon MacBook.

What about the Late 2014 Retina 5K iMac?

This is where the distinction becomes important. The Mid 2014 iMac appears on Apple's Target Display Mode compatibility list. The Late 2014 Retina 5K iMac does not.

That means Apple's first Retina 5K iMac cannot simply be connected to a modern MacBook and switched into Target Display Mode. The same fundamental limitation applies to later Retina iMac generations.

This is particularly frustrating because the computer inside an older iMac may be showing its age while the display can still be excellent. A 27-inch Retina 5K iMac has a native resolution of 5120 × 2880 pixels, which still provides an exceptionally useful desktop workspace today.

Can AirPlay turn an iMac into a second monitor?

On newer Macs, AirPlay to Mac provides another Apple-native option. Apple's main requirements specify macOS Monterey 12 or later and supported Mac hardware. For the standard iMac lineup, this effectively makes 2019 the first regular iMac generation covered by Apple's main AirPlay to Mac hardware requirements.

There is, however, an important nuance. Apple also states that some older Mac models may be able to use AirPlay to Mac at lower video resolutions when AirPlay Receiver is available and configured appropriately. So it is not accurate to say that every older iMac is completely incapable of receiving AirPlay.

Receiving an AirPlay stream is not the same thing as turning a Retina 5K iMac into a native 5K external display.

For users who want to reuse the entire Retina panel as a productive extended workspace, that distinction matters.

Does AirPlay require the same Apple Account?

Not always. Apple allows AirPlay Receiver to be configured for Current User, Anyone on the Same Network, or Everyone. Using the same Apple Account is therefore part of the most restrictive Current User configuration, but Apple also provides network-based access options. So the statement that AirPlay always requires the same Apple ID is an oversimplification.

How to turn an iMac into a real extended display

MacDisplay was designed specifically for this problem. Instead of simply mirroring the same picture on both computers, MacDisplay creates a true extended Mac desktop.

Your MacBook remains the primary Mac. The iMac becomes another independent display: you can move the pointer from one screen to the other, drag application windows onto the iMac and arrange the displays in macOS just like a normal multi-monitor workspace.

Older Macs that cannot use the supported Thunderbolt connection can still use Ethernet or Wi-Fi.

Can a 2017 5K iMac become a second monitor for an Apple Silicon MacBook?

Yes. This is one of the most interesting MacDisplay configurations: you can use a 2017 27-inch Retina 5K iMac as the receiving display and a modern Apple Silicon MacBook Pro or MacBook Air as the source.

The fact that the receiving iMac uses an Intel processor does not prevent MacDisplay from using its Retina display at native 5K resolution. The important distinction is the Mac doing the sending.

The ceiling therefore depends on two things: the Mac sending the desktop and the video capabilities of the Mac receiving it. If the receiving Mac does not have the required video support, the limit stays at native 4K even with an Apple Silicon source. You do not need to work this out in advance: MacDisplay recognises the pair and picks the highest possible preset on its own.

The limit is set by the sending Mac and the receiving Mac together: the 4K ceiling also applies when the receiver lacks the required video support.

What a native 4K ceiling means on a 5K screen

It means it still works, and you still use the whole screen. The extended desktop is there, the iMac becomes a monitor in every respect, and windows move and arrange normally: the picture is simply scaled from 4K to the size of the 5K panel, so it looks slightly softer than native.

It is the difference between "a little softer" and "not possible": the screen stays fully usable, and for text, windows, references and working panels the difference is barely noticeable. If you want the exact sharpness of the panel, you need the combination that reaches native resolution.

What about 8K?

8K is already in the app: you can select and enable it. It is not a configuration we have tested and certified, though, so the result depends on the two Macs you are using: on some pairs it works, on others it does not.

At these resolutions, performance depends heavily on both sides. The source Mac must be powerful enough to generate and transmit such a demanding stream, and the receiving Mac must be capable of processing and rendering it in real time. With two powerful Macs, 8K can be reached; with an older receiving Mac, the limit arrives sooner.

In practical terms: 8K is available and selectable, but should be considered experimental. The sensible way to find out is to try it with the free version on your own pair of Macs.

How to use MacDisplay

Getting started with MacDisplay requires only a few steps.

1. Install and open MacDisplay on both MacsYou need it on the Mac sending the desktop and on the one receiving it.
2. On the Mac you want to use as the second display, select "Become a Monitor"That is the old iMac.
3. On the primary Mac, select "Extend Screen"That is the MacBook you keep working on.
4. Grant Screen Recording permission on the Monitor MacmacOS requires it before the first connection. Also check that third-party antivirus, firewall or security software is not blocking communication between the two Macs.
5. Start the connection on the Monitor MacIt is not mandatory, but we suggest always starting from the Mac acting as the monitor.
6. Then start the connection from the source MacMacDisplay automatically detects the available Mac, establishes the connection and creates the extended display.

The correct monitor preset is also detected automatically, so in most cases there is no need to manually select a resolution, display profile or preset. Manual preset controls remain available for users who need them, but the recommended configuration is to leave automatic detection enabled.

Can I try MacDisplay before buying?

Yes. MacDisplay has a free version that does not expire. There is no account to create and no credit card is required.

The free version currently allows display sessions of up to 10 minutes, followed by a 60-second cooldown, with up to 60 minutes of use every 24 hours. The full license removes those limits and is available as a one-time purchase rather than a subscription.

This allows you to test something particularly important before buying: your exact MacBook, your exact iMac, your connection and the resolution you want to use.

MacDisplay vs Luna Display and Duet Display

Other Mac-to-Mac display solutions exist. Luna Display supports using a Mac as a second display and can reach 5K on compatible configurations, but its 5K setup requires dedicated Luna hardware. Duet Display also supports using an iMac as another display and offers software-based display extension through its own plans.

MacDisplay takes a deliberately narrower approach: it is designed specifically around Mac-to-Mac display extension. No dedicated hardware. No MacDisplay account. No cloud relay required for the display connection. Native resolutions up to 6K with compatible Apple Silicon source Macs (up to 8K depending on the performance of both Macs). And a free version that does not expire.

Should you replace an old iMac or reuse its display?

If the display is still in good condition, reusing it can make a lot of sense. The computer inside an older iMac and the Retina panel attached to it do not have to become obsolete at the same time.

A 2015 or 2017 iMac may no longer be the Mac you want to use every day, while its 4K or 5K Retina display can still provide an excellent workspace. Instead of leaving the iMac unused or buying another monitor, you can give that display a second life.

Your old iMac can become the monitor your new MacBook needs.

Frequently asked questions

MacDisplay Published 30 August 2026