When do you need to use an em-dash?

The em-dash is the most common dash seen in fiction writing. It’s called an em-dash because it’s about the same width as a printed capital letter M. When you use an em-dash, you should only use one at a time.

The em-dash is excellent at setting off parenthetical thoughts. Use one before and one after the additional information:

• Albert ran—well, more like stumbled—across the finish line.
• I couldn’t believe—or even comprehend—what I was seeing.
• Jenna slurped down the rest of her coffee—no cream, no sugar—then tossed the empty cup into the trash.

As you can see, the em-dashes in these sentences perform a similar function to parentheses. They add greater context to a detail mentioned in the sentence, though they aren’t integral parts of the sentence by themselves. Therefore, they’re set apart with em-dashes.

Em-dashes can be used alone to indicate a moment of surprise in writing:

• The baby cried and cried and—she stopped. Was someone playing “Baby Shark”?
• The match touched the wick, the fuse ignited—bang! The explosion boomed through the night.
• I smiled, breathed in the fresh air, and—coughed. Where had the smoke come from?

And they can also be used in dialogue to signify an interruption:

• “And then I went to school but school was closed because it was a snow day, so I sledded all the way back home and made myself a hot chocolate, but then the power went out, so I—”

“Okay, okay. You had a rough day. I get it!”

Like any tool, it’s best not to overuse em-dashes in our writing. If we do, our prose can become clunky and unsurprising. The old aphorism rings true here: less is more.