How Quickly Will Your Email Get A Response?

A new study measures millions of emails to see how long it takes for people reply to each other, and how much they write.

In 2013, 183 billion emails were sent every day, according to the technology-research firm Radicati. The firm predicts that by 2017, it will be nearly 207 billion. This is a gold mine of information for communications research, but an overwhelmingly daunting one. Attempting to analyze all of it would be like Scrooge McDuck diving into an ocean of gold, and then drowning in it.

But as an email becomes an increasingly integral part of the puzzle of human communication, understanding how people use it becomes more important as well. And a new study, the largest study of email yet, manages to bottle and measure a pretty big portion of that gold ocean.

Researchers from Yahoo Labs and the University of Southern California Information Sciences Institute analyzed 187 million emails sent between 2 million unique users to see how long it took people to reply, how long their replies were, and how that changed depending on factors like time of day and who was doing the emailing. (Caveat: They were all sent using Yahoo Mail.)

The researchers only included messages sent from one person to one other, no group emails. And to eliminate the possibility of including bots or spam, they only looked at email threads between people who emailed each other at least five times during the course of the study, which lasted “several months.” (The paper doesn’t specify exactly how many.)

With that in mind, the results of the study indicate that if you are a real person, emailing one other real person whom you know, chances are you’ll get a response within the same day. In the study, this was the case 90 percent of the time. Half the replies came within 47 minutes, and the most likely response time was two minutes.

But they’re not going to write you a novel. Half the replies are under 43 words, and the most common length was just five words long. Also, the faster you get your reply, the shorter it’s likely to be. With a weird exception—once emails get longer than 200 words, they take slightly less time to write, possibly because people who are that verbose in emails are more likely to be comfortable writers. These people may also be writing the 30 percent of emails that were 100 words or longer.

Emailing also seems to follow its own sort of circadian rhythm, waxing and waning pretty much in time with the standard work-week. Weekday emails get longer and faster responses than those received on the weekend, and emails sent at night take longer to get responses than those sent during the day. People also send longer responses to morning emails than afternoon or evening emails.

Maybe that’s because if you catch them in the morning, your email is just a single snowball rolling down the mountainside, one that can be easily caught and tossed back. As the day goes on, all the snowballs become an avalanche and the best someone can do is dig a little pocket of air to breathe in. As people’s “email load” gets higher, the study found, they respond to more emails, more quickly, with shorter messages. But it’s often not enough to keep up.

“As the email load increases, users reply to a smaller fraction of their emails, from about 25 percent of all emails received in a day at low load to less than 5 percent of emails at high load (about 100 emails a day),” the study reads.

As might be expected, there are generational differences in how people deal with this digital deluge. In general, teens send the fastest, shortest messages—their fingers are nimble and their brains attuned to the medium. It takes them 13 minutes on average to reply to an email. Young adults (20 to 35 years old) take 16 minutes on average, adults (36 to 50) take 24 minutes, and people 51 and older take 47 minutes. The teens of course are unfazed by email load, and respond to the same fraction of messages no matter how many they get. The older people get, the less they seem able to deal with the mounting pile of little demands on their time, which I’m having trouble not seeing as a metaphor.

Anyway, if you want a response to your email as fast as possible, send it to a teen in the morning on a weekday! Or don’t—they need to focus on homeroom.