I'm Dmytro, the founder of KissMyPost, and I spend my days counting things in Reddit data. The question I kept hearing was whether the em dash gives away ChatGPT, so I counted it. I checked every long post and comment in 100 large English-language subreddits. Here is what I found, and what the data can't tell you.
The short answer
In 100 large English-language subreddits, the share of long posts containing an em dash rose from 0.70% in early 2021 to 6.53% in Q2 2025, more than nine times the early 2021 level. Long comments in the same subreddits went from 0.68% to 1.32%.
The climb began in August 2024, about 20 months after ChatGPT launched, and it doesn't match the way phone autocorrect changed Reddit's punctuation in 2017. The rise is concentrated in posts, where text written elsewhere gets pasted in, which fits AI-assisted writing better than a keyboard change. It can't tell you whether any particular post was written by AI.
What we counted
We took 100 large English-language subreddits and looked at every text post and every comment of at least 200 characters written there from January 2016 to September 2026. That comes to 15,817,377 posts and 241,541,185 comments. For each one we checked a single thing: does it contain at least one em dash (Unicode U+2014), anywhere in it. For posts, the title counts too. Hyphens and en dashes don't count.
The climb started in August 2024, not when ChatGPT launched
ChatGPT became public on November 30, 2022. In that quarter, 0.83% of long posts in our sample had an em dash, about where the share had been all year. Over the next 18 months it crept up to 1.19%.
The jump came in August 2024. In July, 1.28% of long posts had an em dash; in August, 1.95%; by December, 3.12%. In July 2025 it reached 6.83%, the highest month in more than ten years of data.
We can't tie the August jump to any particular release. Timing is all this data shows: it came three months after OpenAI released GPT-4o and about 20 months after ChatGPT launched.
Comments rose far less
Reddit comments are mostly typed straight into the comment box, on the same phones and keyboards people use for posts. If a keyboard or an app had started inserting em dashes on its own, comments would show it too.
Between Q2 2024 and Q2 2025 the share of long comments with an em dash went from 0.65% to 1.32%, a gain of 0.67 percentage points. Long posts gained 5.35 points over the same year, going from 1.19% to 6.53%.
Posts are where people paste in text they wrote somewhere else: a story drafted in a notes app, a launch announcement cleaned up in a chatbot. That's the most likely reason the two lines split, though it's an inference from the pattern and not something we can observe.
Is it autocorrect?
It has happened once. In September 2017 Apple shipped iOS 11 with Smart Punctuation turned on by default, which converts two typed hyphens into an em dash. Our data picks it up: em dash share rose in both posts and comments, while the double hyphen fell in both. When the keyboard changes, both kinds of text move together.
The 2024 rise looks different. Double hyphens in posts were at 0.40% in Q2 2024 and 0.40% a year later, and comments gained 0.67 points against 5.35 for posts.
It showed up everywhere
72 subreddits in the sample had at least 300 long posts both in 2021 and in 2026. The em dash share in posts went up in all 72 and at least tripled in 60. In the median subreddit, 0.50% of long posts had an em dash in 2021 and 4.00% in 2026. For comments the median went from 0.42% to 0.81%.
In r/SideProject, where people announce things they've built, 29.3% of long posts in 2026 contain an em dash, up from 2.0% in 2021. r/writers started high, as you'd expect from people who care about punctuation, and still went from 2.7% to 13.8%.
After the peak
By month, the peak came in July 2025, when 6.83% of long posts had an em dash. In August the share fell to 5.70%, 17% lower in a single month, and in December 2025 it reached 4.78%. August 2025 is the month GPT-5 became ChatGPT's default model. In mid-November, OpenAI's CEO said ChatGPT now follows custom instructions to leave out em dashes, and the following month was the lowest since the peak.
That's the order of events. This data can't show that either change caused the drop. In 2026 the monthly share has stayed between 5.09% and 6.26%, still seven to nine times the early 2021 level.
What this data can't tell you
- An em dash doesn't mark a post as AI-written. People typed them long before chatbots: 0.70% of long posts in early 2021, and far more in some communities. The change shows up across millions of posts and says nothing reliable about any one of them.
- Timing isn't cause. The rise came while AI writing tools were spreading, and the comment and double-hyphen checks rule out the obvious alternatives we could test. Other explanations are still possible.
- October 2025 looks odd. Its em dash share in posts (6.39%) sits well above September (5.34%) and November (5.56%), and we haven't found out why. It's left out of the monthly chart. Nothing in the article depends on that month.
Full method and data
The full method, every table and the CSV files behind these numbers are on the original study: The em dash and ChatGPT: what ten years of Reddit posts show.
More studies from the same Reddit data are at kissmypost.com/research.
Top comments (0)