Can I use my old iMac (2015) as a monitor for a new MBP?

[Gustoso]

I'm currently on a 2015 iMac. I'm upgrading to a M5 Pro MBP as soon as they drop (Jah willing). Having a laptop will be much better for my use cases, but at home I find I've come to really enjoy the extra screen real estate. This thing has a 27" 5k display. Hard to believe it's almost an 11-year-old machine at this point.

Anyway, can this be done? The iMac doesn't have HDMI but does have Thunderbolt 2. Any tips appreciated, thanks.

 

[FreakinEurekan]

There's no simple way. The 2015 is too new to support Target Display Mode (that ended with Retina displays), but it's too old for AirPlay to Mac (2019+ models).

There are some 3rd party software and/or hardware options, and they will "Work" but framerate is limited.

 

[PaulD-UK]

Quote: ‘There’s no simple way.‘

The more complicated way involves opening the iMac, removing the original electronics, and installing a new video driver board, costing around $190-225…
This will connect via USB-C to your new MBP and give you a 5K screen image as good as your old iMac did.

Not for most people, but it is the only option giving performance as good as the screen is capable of.

DIY 5k Monitor - success :-)

From @SubDriver (24 May 2025) Converting iMac 5K Retina Display to a Standalone 5K Display I believe the details in the table below are accurate, but I am not 100% certain. I tried my best to use reputable sources (datasheets, etc.) for the info in the table, but some information comes from...

forums.macrumors.com

 

[Basic75]

There's also the built-in screen sharing which, on a fast network, should be good enough for text and office things but not for multimedia or gaming.

 

[Fishrrman]

Considering the money, time, and potential trouble you may encounter "converting" the iMac into an external display, it's not worth it.

Get a 27" 4k or 5k display, and be done with it.
Much less trouble and things should work out-of-the-box...

 

[sotosoul]

I think YouTuber Snazzy Labs uploaded a video of a similar project, where he replaced the guts of a 2017 27" iMac with LCD screen electronics and power circuitry. Look it up, it's a really cool video to watch, however, I don't see it as a realistic solution for most of us mere humans.

It's probably easier (and likely cheaper) to sell the iMac and just buy a screen.

That being said, I would argue that your iMac will still be relevant at home as a standalone computer, especially if you're using iCloud or another syncing solution. I am a huge proponent of squeezing every singe drop out of our vintage electronics!

 

[startergo]

Yes there is a way. Don't know how fast the Thunderbolt 2 is but should be ok.

Use Your iMac as a Monitor: A Step-by-Step Guide [2025]

Looking for a way to use your old iMac as a monitor? This guide walks through how to use your gorgeous 5k iMac display for your Mac or PC.

astropad.com

In full disclosure, we are the creators of Luna Display, but we added iMac support for a reason – nothing existed for using an iMac display at full 5K resolution! At Astropad, we like to solve problems we have ourselves, and Luna Display is no exception.

I recommend connecting your iMac to your primary Mac using a USB cable – it’s what I use everyday. Unless you have a recent iMac, you’ll want to buy a USB-C to USB-A cable, this is the cable I use with my 2015 iMac and 2021 M1 MacBook Pro.

 

[Brian33]

I'm currently using the Luna Display solution and thought I'd mention my experience in case anyone's interested.

It works pretty well. It's not as good overall as having an actual external monitor, but I'm happy with it, for the ease and the price.

The Luna Display device is plugged into my 2024 Mac Mini with M4 PRO chip, and my old 2015 27" iMac is acting as my auxiliary display. Currently I'm connecting the two Macs via their respective Ethernet cables to my network switch. So, I get only a 1 Gb/s connection. It did work well with peer-to-peer WiFi also, but the Ethernet is preferred. I played around with using a USB-C cable, which should give a 5 Gb/s connection (the best the 2015 iMac USB 3.0 port will do), but, if I remember correctly, I had to plug the cable into a Thunderbolt 5 port on the Mini (in addition to the Luna device needing to be in a Thunderbolt 5 port) to get it to work. I didn't want to use up two TB5 ports. (I might play around with that again to verify.)

The best connection (20 Gb/s) would be iMac's Thunderbolt 2 <---> Apple Thunderbolt Adapter <---> Mini's Thunderbolt 5, but I decided the $90 (EDIT $49) or so for the adapter wasn't worth it.

Pros:

• Can do real 5K resolution -- so static text is nice and sharp!
• Mouse pointer flows seamlessly to it.
• When I wake my Macs (see below) or restart the Luna software, application windows return to their previous locations on the auxiliary display (the iMac), just where they should be.
• Reliable -- no software glitches.
• Not too expensive -- around $100.
• Easy to set up.

Cons:

• Motion is somewhat jumpy on the aux iMac -- dragging a window or scrolling text is not smooth. The degree of this effect will depend partly on how you connect the two Macs. I definitely wouldn't try any sort of gaming on it, but it is great to have a game's wiki page open on the side while my game is full-screen on my Studio Display! Also fine for email and Messages.
• The Luna Display device uses up a Thunderbolt port on the Mac Mini (the front USB-C ports do not support display output). Astropad says not to, but I tried plugging it into a Caldigit TB 5 hub anyway... it didn't seem to work reliably.
• The auxiliary "monitor" (my iMac) doesn't sleep when my main Mac Mini sleeps. After much experimenting, I've proven to myself that both machines will sleep if I follow this procedure: put the iMac to sleep with Cmd-Option-Eject key sequence (I have old keyboards with the Eject key), then do the same on my main Mac Mini. You should be able to set your own keyboard shortcut if you like. Or, you can terminate the Luna software on the main Mac then hold Esc for a few seconds on the auxiliary Mac's keyboard.
• When you return, you need to wake up and log into two Macs (faster if you have fingerprint reader keyboards!).
• You still have a full macOS installation on the aux "monitor" (do you back it up?) and that extra keyboard.
• My 2015 iMac has the dreaded pink tinge around the borders. : (

 

[startergo]

I use thunderbolt connection with Luna and the results anre excellent. Virtually no lag.

 

[Brian33]

I use thunderbolt connection with Luna and the results anre excellent. Virtually no lag

Thank you for that. I may give that a try. Especially because I misremembered the cost of the thunderbolt adapter.