How to Use Your iMac as a Monitor: A Full Guide

Can You Use an iMac as a Monitor?

Yes—but it depends on the iMac model and the devices you want to connect.

Apple allowed certain iMacs to be used as external displays via a feature called Target Display Mode (TDM). This only works with iMacs released between 2009 and mid-2014.

Newer iMacs running macOS Catalina or later do not support this feature. Apple removed TDM entirely, likely due to changes in display architecture and internal GPU dependencies.

Additionally, using an iMac as a display for a PC requires different methods altogether—TDM won’t work. In this case, third-party software or hardware solutions become necessary.

So, before starting, identify your iMac’s model and macOS version. If it’s compatible, using it as a monitor can save space and cost. If it’s not, alternatives exist but come with trade-offs in quality, latency, and complexity.

Requirements for Using an iMac as a Monitor

Here’s what you need for Target Display Mode:

• Compatible iMac models:
  • 27-inch iMac (Late 2009, Mid 2010) — Mini DisplayPort
  • iMac (Mid 2011 to Mid 2014) — Thunderbolt
• Mac source device (MacBook, Mac mini, etc.) with:
  • macOS High Sierra or earlier (for best compatibility)
  • A Thunderbolt or Mini DisplayPort
• Cable:
  • Thunderbolt or Mini DisplayPort to Mini DisplayPort
• Keyboard:
  • Apple keyboard (or one with a Command + F2 key combo)
• Same macOS generation: macOS versions should be close between iMac and the source Mac to avoid connection issues.

Newer iMacs (post-2015) or those with Retina displays don’t support TDM. Always check Apple’s specs before buying cables or setting things up.

How to Use an iMac as a Monitor for Another Mac

Using Target Display Mode

1. Turn on both Macs and log in.
2. Connect them using the correct Thunderbolt or Mini DisplayPort cable.
3. Press Command + F2 on the iMac keyboard.

Your iMac should instantly mirror or extend the display from the other Mac.

To exit, press Command + F2 again or unplug the cable.

Important Notes:

• Both Macs must be awake.
• TDM only mirrors the display; no sound is transmitted.
• iMac acts as a display only, not as a secondary computer.

Using Third-Party Apps or Workarounds

If TDM isn’t an option, consider:

• Luna Display (hardware dongle that turns iMac into wireless or wired second screen)
• Duet Display (app-based solution with moderate latency)
• Sidecar (only works with iPad, but sometimes confused as iMac-compatible—it isn’t)

These tools are helpful but may reduce display quality or introduce lag. They also often require newer macOS versions and good Wi-Fi.

How to Use an iMac as a Monitor for a PC

Using an iMac as a PC monitor is trickier.

TDM won’t work with Windows. Instead, you need:

• A video capture device (HDMI-to-USB adapter)
• Software like OBS or SpaceDesk
• A fast network or wired setup to minimise lag

Alternatively, you can use remote desktop tools:

• Chrome Remote Desktop
• AnyDesk
• Parsec

These allow screen sharing but aren’t ideal for tasks needing low latency, like gaming or video editing.

If your goal is productivity (e.g., text work or browsing), these methods are acceptable.

Common Problems and Fixes

iMac doesn’t enter Target Display Mode?

• Confirm Command + F2 is pressed on iMac, not the other Mac.
• Check cable compatibility.
• Restart both devices.

Screen stays black?

• Ensure source Mac’s display is active.
• Try toggling Command + F2 again.

No sound?

• TDM only transfers video, not audio. Use external speakers or route sound via AirPlay if supported.

Macs running different macOS versions?

• Update both to the closest supported version or downgrade if needed.

Still not working? Your model may not support TDM at all.

Pros and Cons of Using iMac as a Monitor

Pros:

• Saves money on buying an external monitor
• High-quality Retina display (if compatible)
• Seamless integration within Apple ecosystem

Cons:

• Limited to older models
• No audio support
• Doesn’t work with M1/M2 Macs or modern macOS
• Requires specific cables and ports

If you have a compatible setup, it’s a good solution. But for many, alternatives may be easier.

Alternatives If It Doesn’t Work

If your iMac doesn’t support TDM:

• Buy a dedicated monitor: Modern 4K monitors are affordable and widely compatible.
• Use screen sharing: For basic tasks, apps like Chrome Remote Desktop or macOS Screen Sharing are viable.
• Repurpose the iMac: Turn it into a media center, server, or digital photo frame.

If your goal is productivity, not performance-heavy tasks, these workarounds can be effective.

Final Thoughts

Using your iMac as a monitor is possible—but only under the right conditions.

TDM works well but is limited to older iMacs and macOS versions. Newer systems will need third-party tools or remote access workarounds.

Before starting, check model compatibility, cables, and macOS versions. If it’s too complex, it might be time for a proper monitor upgrade.

For a quick setup that “just works,” Target Display Mode on a supported iMac is still the best route.

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