Recently I purchased a 4K monitor for my Mac. I have a MiniDP to HDMI 2.0 converter and a HDMI 2.0 cable. I connected my late 2015 Retina iMac to the external monitor. I was able to get 4k@30hz on my external display. However, I was unable to achieve the 60hz refresh rate.

After some research I figured that late 2015 iMacs with the thunderbolt 2 ports should support 4k@60hz video output. I can't seem to figure out why I can't get the 60 Hz refresh rate.

When I open System Preferences, the Refresh Rate drop-down menu is gray.

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Mac Configuration: iMac (Retina 4K, 21.5-inch, Late 2015) MacOS: Catalina

I connected the same monitor to my 2018 MacBook Pro using a USB-C to HDMI 2.0 cable. My MacBook Pro was able to drive the display at 4k@60hz.

Thank you for your time and consideration!

  • What MiniDP adapter are you using? Most of them only support 4k @ 30 (Belkin, Monoprice, etc) Commented Apr 17, 2020 at 3:18

2 Answers 2


The late 2015 21.5-inch Retina 4K iMac is fully able to drive a 4k display at 60 Hz. The monitor you have also lists that it supports 4k at 60 Hz.

The problem here must then either be your HDMI cable or your DisplayPort to HDMI converter.

I would suggest simply trying a different cable/converter.

The easiest to get working is to get a simple mini-DisplayPort to DisplayPort cable, as the monitor has a DisplayPort input. This way you haven't got the converter as an extra point of failure.

  • Thank you for your answer. I have tried using a MiniDP-> HDMI converter + HDMI 2.0 cable. I also tried MiniDP -> HDMI cable (no converter). Both have failed. I will try the Mini-DP to DP port then. Thank you very much!
    – NeilNie
    Commented Apr 16, 2020 at 19:56
  • Thank you for the answer, this resolved my issue!
    – NeilNie
    Commented Apr 22, 2020 at 23:16
  • Coming to this a bit late, but my display is stuck at 24Hz and I am using a direct mDP to DP cable that supports 4K@120Hz. Could there be any other reasons for the refresh rate limit? I am also on a late 2015 21.5" iMac. Using EasyRes, these are the options I'm seeing (60Hz only becomes available at 720p): i.imgur.com/lnnXOVk.png
    – kayoz
    Commented Apr 28, 2022 at 17:29
  • What display is it?
    – jksoegaard
    Commented Apr 28, 2022 at 21:23
  • Sorry, I did not get a notification for the comment. The display is a Gigabyte M28U and I'm able to get 144Hz from another computer.
    – kayoz
    Commented May 13, 2022 at 8:12

Your issue is most likely caused by your MiniDP adapter. Most of them do not support greater than 4k@30hz. Something like this that is specifically compatible with that high data rate should fix the issue:


  • I appreciate your response. I specifically found a MiniDP adapter on Amazon that support 4k@60hz. The MiniDP ->HDMI cable I purchased also explicitly states it support 4k@60hz.
    – NeilNie
    Commented Apr 17, 2020 at 14:23
  • This is the adapter that I am using: amazon.com/gp/product/B00PJ3LSIG/…
    – NeilNie
    Commented Apr 17, 2020 at 14:24

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