How to change the main display on a Mac
Short answer: open System Settings → Displays, select the monitor you want, and set Use as to Main display. Or click Arrange… and drag the white menu bar to that screen. The menu bar, login window and new windows move to it. The Dock still follows the pointer to other screens unless you pin it.
On this page
What the main display does
The main display is where macOS puts the things there is only one of: the Dock by default, the login window, and new windows and dialogs for many apps. When "Displays have separate Spaces" is turned off, only the main display has a menu bar.
Choose it in Displays
- Open System Settings → Displays.
- Click the monitor you want to be the main display.
- Set Use as to Main display.
Or drag the menu bar
- In System Settings → Displays, click Arrange….
- One of the screens shows a thin white bar along its top — that is the main display.
- Drag the white bar onto the other screen, then click Done.
While you are there, line the screens up the way they sit on your desk, so the pointer crosses between them where you expect.
The Dock still moves
Changing the main display moves the Dock there, but not permanently: rest the pointer at the bottom of another screen and the Dock jumps across. macOS has no setting to stop it. Okie Dockie keeps the native Dock on the display you choose — see stop the Dock moving to your other monitor.
When it resets
macOS remembers the choice for each combination of displays. If it resets, it is usually because a dock or adapter makes the monitor appear as a new display, or the monitor was connected to a different port. Connecting through the same port each time keeps the arrangement.
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Frequently asked questions
How do I set the main display on a Mac?
System Settings, Displays, select the monitor, and set Use as to Main display — or drag the white menu bar in Arrange.
Why does my Mac keep changing the main display?
A dock or a different port can make the monitor appear as a new display. Use the same port each time.
Does changing the main display move the Dock?
Yes, but the Dock still moves to other screens when the pointer reaches their bottom edge.
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