Screenwriting : Characters Speaking at the Same Time by Imo Wimana Chadband

That pretty much works for me. (If it's a two shot, the Director may need to mic each character separately and blend in post - not a big deal.)

Ah, nice! Guess I'm on the right track. Thanks Doug!

that's how I do it. I use writer duet and when you click on multiple character dialogue function, it lays it out like that.

Yes, dual dialogue format as per the software you're using.

Don’t think you need “at the same time” dual character implies that. It’s no wrong just saves you a line.

Rather than writing "at the same time", why don't you write something that makes them respond that way. An action line. i.e. "the mirror falls off the wall".

If you do not care for dual dialogue there are other options... you can simply use dialogue format per usual or put two character names together if, say, two characters are saying the exact same thing at the same time.

Examples from The Screenwriter's Bible:

SAM AND JO

(together)

Huh, what?

Or

SAM AND JO

(simultaneously)

Huh, what?

Or if say one character's dialogue overlaps another character's, for example, using Imo's post above:

ANDREW

Creepy.

ARIEL

(overlapping)

Nice.

I actually like this version better than dual dialogue. Seems a better fit acknowledging the scene context that Andrew at first is standing alone and Ariel has come up behind him without him realizing and she too witnesses a new crack split across the mirror. ;)

Beth Fox Heisinger well stated..

Oh! Beth Fox Heisinger that's a different take on it, but not a bad one at all. Personally, I don't have a set preference on having to use dual dialogue, it's the only way I knew thus far. I'll joggle this idea as well and see which works best in the scene. Thanks Beth!