How to set your arrangement
- Open Displays settings. Choose Apple menu › System Settings, then click Displays in the sidebar.
- Click Arrange. The button appears only when an external display is connected. Each display is shown as a rectangle.
- Drag displays to match your desk. Put the rectangles where the screens physically are, left or right, above or below. Line up their edges so the pointer moves across where you expect.
- Move the menu bar to your main screen. Drag the white bar at the top of one rectangle to another display. That display becomes the main one.
- Or use "Use as". Back in Displays, click a monitor's name and choose Use as › Main display. The same menu lets you extend or mirror instead.
Holding Option while dragging one display onto another mirrors them. If your screens suddenly show the same thing, that's what happened. Drag them apart again or change Use as.
Why the arrangement resets
- Different ports or docks. The Mac remembers arrangements for the combination of displays it sees. A different port or dock can look like a new combination, so you get a default arrangement instead.
- Identical monitors. Two monitors of the same model can be hard for the Mac to tell apart, so left and right can swap.
- Adapters that hide the monitor's identity. Some cheap adapters and docks don't pass along the monitor's details, so every monitor behind them looks the same.
- Sleep disconnects. If a monitor drops off during sleep and reconnects in a different order, the arrangement can change with it.
Make it stick
| Problem | Fix |
|---|---|
| Monitors swap sides | Plug each monitor into the same port every time; label the cables |
| Menu bar on the wrong screen | Drag the menu bar in Arrange, or set Use as › Main display |
| Pointer exits the wrong edge | Line up display edges in Arrange to match the physical screens |
| Screens show the same picture | They're mirrored; change Use as to extended |
| Resets with one dock but not another | Update that dock's firmware, or connect the monitor directly |
Arrangement versus window layout
The arrangement only tells macOS where your screens are. It doesn't decide where each app's windows go, so even with a perfect arrangement your windows can still end up piled on one screen after a disconnect. Fixing the arrangement first makes everything else more predictable.