How to Connect a Mac to an External Monitor

The monitor is plugged in and showing nothing, or it shows an exact copy of the Mac's own screen. A blank second display is nearly always a cable, an input source, or an arrangement setting rather than a failed port. Displays settings handle the rest once the signal arrives.

Match the cable to the ports at both ends

Recent Macs send video over USB-C or Thunderbolt, and some models also have a full-size HDMI port. Check what inputs the monitor has, then use a cable that fits both ends or a USB-C to HDMI or DisplayPort adapter. A USB-C cable rated only for charging and data carries no video, which produces exactly the same blank screen.

Power the monitor on and select its input

Switch the monitor on before connecting the Mac, then use the monitor's own buttons or remote to set the input source to the port you plugged into. A monitor sitting on the wrong input looks identical to one receiving no signal at all.

Arrange the screens in Displays

Open System Settings, Displays. Both screens appear at the top. Select the external one and set Use as to Extended Display, or to Mirror if you want the same picture on both. Click Arrange and drag the blue rectangles so they sit the way the screens sit on the desk, then drag the white bar onto whichever display should carry the menu bar and be treated as the main one.

Reveal Detect Displays if nothing appears

If the external screen never shows up, hold Option while the Displays pane is open. A Detect Displays button appears at the lower right; click it to make macOS probe the port again. On macOS Monterey and earlier the same button sits in System Preferences, Displays.

Set resolution and refresh rate per screen

With the external display selected, pick a resolution from the list and choose a Refresh Rate if the menu appears. Go as high as the monitor supports; a mismatch here causes flicker or a picture that drops out every few minutes.

Some Macs drive only one external display. MacBook Air and base-model MacBook Pro models support a limited number of external screens, often just one. A second monitor on those machines needs a DisplayLink dock with its driver installed, not another adapter.

A closed-lid setup needs three things. Power connected, plus an external keyboard and an external mouse or trackpad. Without them, closing the lid puts the Mac to sleep and the external screen goes dark with it.