Create pane occupying half of the screen

Question

Let's say I have an arbitrary layout of tmux panes in a window.

+------------------------------+
|                              |
|                              |
|                              |
|                              |
|     Some arbitrary layout    |
|                              |
|                              |
|                              |
|                              |
+------------------------------+

What I want to do is to split this window in half (with a horizontal split), such that I create a new pane occupying half of the screen. Essentially I want to end up with the following.

+--------------+--------------+
|              |              |
|              |              |
|              |              |
|     Same     |              |
|    layout    |   New pane   |
|   as before  |              |
|              |              |
|              |              |
|              |              |
+--------------+--------------+

Is there any way to accomplish this? Optimally I would also like to open Neovim in the new pane.

Answer 1

Assuming Ctrl-B is your binding key:

Ctrl-B + %

Or if you want use this in your .tmux.conf:

split-window -h