Snap windows side by side on a Mac by holding Option

Why it happens

Like Snap on Windows, your Mac can tile windows into halves and quarters of the screen. With plain edge dragging on, windows can snap when you didn't mean them to. The Option setting lets you tile only when you hold the key, so normal dragging stays normal.

How to fix it

1. Open the Apple menu, choose System Settings, and click Desktop & Dock. Scroll down to the Windows section.

2. Turn on Hold ⌥ key while dragging windows to tile.

   Desktop & Dock›Windows›Hold ⌥ key while dragging windows to tile

3. If you only want tiling when you hold Option, turn off Drag windows to left or right edge of screen to tile in the same section.

   Desktop & Dock›Windows›Drag windows to left or right edge of screen to tile

4. Now try it. Start dragging a window by its title bar, hold Option, and move it towards the left or right side. An outline shows where it will go. Let go of the mouse and the window fills that space.

Still not fixed?

1. Using a keyboard made for Windows? The Alt key works as Option on a Mac.

2. Prefer keys to dragging? Click the window, then choose Window > Move & Resize in the menu bar. Each layout lists its shortcut there, such as Fn-Control with an arrow key.

   Menu bar›Window›Move & Resize

3. Tiled windows have a small gap between them. To make them touch, turn off Tiled windows have margins.

   Desktop & Dock›Windows›Tiled windows have margins

4. Some apps only allow certain window sizes, so they may not fill a half exactly. If no window will tile at all after a restart, contact Apple Support.