For Americans of all political persuasions, the last few months have been a nervous, unsettling time. Tensions that were buried under the surface are out in the open. Scary possibilities that seemed remote now feel plausible. If you're a news junkie or the sort of person who gets into arguments on social media, it can be hard to fall asleep, knowing the next breaking story or tweet could mean another major upheaval.

On the other hand, it's a great time to be a company that helps people deal with their unwanted anxiety. The week after the presidential election, Calm, the maker of an eponymous guided-meditation app, saw its rate of sales spike by more than 50 percent, according to co-founder Michael Acton-Smith. "There are a lot of very anxious, stressed people out there," he says.

He used to be one of them. Calm is Acton-Smith's third startup. His first was the online retailer His second, Mind Candy, made a video game that had 80 million registered users.* Despite the success, Acton-Smith found it hard to relax. He suffered from fatigue, headaches, and "the whirring mind of an entrepreneur, waking up at 4 a.m., thinking of all these things."

Acton-Smith had long had a vague sense a mindfulness practice was something that might help him. With a friend, Alex Tew, he had even purchased the domain in 2011 with plans to start a digital content business around mindfulness; Tew was an avid practitioner. But it wasn't until 2014 that Acton-Smith, during a long sabbatical, finally dove into the literature on meditation and began practicing it himself.

Once he experienced the benefits firsthand, he was all in. He joined Smith in San Francisco, where they set out to create products that offered the benefits of simple mindfulness training--restful sleep, improved focus, relief from stress--without the hippie-ish spiritual or cultural trappings that sometimes put people off.

Making it a habit

Calm's core product is The Daily Calm, a 10-minute guided meditation on the app led by Tamara Levitt, the company's head of content, who has been studying various mindfulness practices for more than 25 years. Each day's meditation emphasizes a different aspect of mindfulness. After much debate, Acton-Smith, Tew, and Levitt agreed the meditations should only be available for that day and then disappear.

It turned out to be a crucial decision, Acton-Smith says. The offering encourages users to adopt Calm as a true daily habit, rather than stockpile the lessons for hypothetical later use like those back issues of The New Yorker on your nightstand you tell yourself you'll read someday. The idea of disappearing content also nicely echoes the mindfulness principle of acknowledging a thought and then letting it go. (Calm now archives a small number of its most popular Daily Calms.)

Without raising any outside money, Calm has become "very profitable," says Acton-Smith. It booked $7 million in revenue in 2016--app subscriptions cost $12.99 per month, or $60 per year--and anticipates more than $20 million this year. More than 8 million people have downloaded the app, and while some content themselves with the limited free offerings, "I've been amazed how comfortable people are paying" for the premium subscription-only tier, he says.

Besides the Daily Calm, the company's offerings include nature scenes and soundscapes, and "Sleep Stories," short, soporific tales read in a lulling voice. There's a Calm coffee-table book, and eventually Acton-Smith plans to do apparel and possibly even a Calm-themed hotel. He believes there's an opportunity to build a brand that will be "the Nike for the mind," likening the public awareness of meditation today to the state of exercise in the 1960s, before the jogging and aerobics fads. "I think we're right at the start of a new wave that's developing around mental fitness," he says.

It only helped, Acton-Smith says, when a competitor, Headspace, raised $30 million in 2015. Prior to that, he says, investors regarded mindfulness as a niche interest. Now, "People realize this is not niche. This is extremely mainstream." That said, Calm isn't eager to follow suit: "We're quite excited about continuing to grow under our own steam," he says.

Acton-Smith is an avid Calm user himself and reports much improved sleep since his Mind Candy days. A regular meditation practice is an asset to anyone doing a startup, he says. "It helps smooth out the huge highs and crushing lows that come with being an entrepreneur. No one wants to follow a leader who's screaming one minute and stressed and upset the next."

Of course, it's partly thanks to such a leader that Calm has become so popular since November. It could be a very profitable four years.

*Correction: Owing to a transcription error, the original version of this story said Moshi Monsters had 18 million registered users, rather than the correct number, 80 million. This story has also been edited to reflect the timing of Michael Acton-Smith's purchase of and his role at Mind Candy.