The idea of the four-day workweek is having a bit of a moment. A trial of reduced hours in Iceland just returned promising results, Kickstarter is giving a reduced workweek a try, and thanks to the pandemic-related shake-up of business practices it seems that jobs listings touting shorter hours are (modestly) on the rise

All of which should make Charlotte Lockhart and Andrew Barnes happy. As the former marketing director and CEO of New Zealand firm Perpetual Guardian, the pair were pioneers of the four-day workweek concept back in 2018 when they ran a successful trial that showed cutting hours at their business led to a 20 percent spike in productivity. They've since teamed up to form "4 Day Week Global," a campaign to try to convince other firms to give a four-day workweek a try. 

But while Lockhart and Barnes are no doubt excited about the growing momentum behind the idea, they told Insider recently that they're concerned the hype is getting out in front of reality. While reduced working hours have many benefits, trimming workweeks isn't without costs and tradeoffs. And while they may be enthusiastic evangelists of four-day workweeks, they want to explode a handful of myths that can trip up bosses making the switch to shorter hours. 

1. It's just another name for a 3-day weekend.  

The term four-hour workweek has instant appeal because it conjures images of three-day weekends, and who wouldn't like a longer break each week? But as charming and clickable as the term "four-day workweek" might be, Lockhart insists it's actually a bit of a misnomer. The policy is essentially about reducing the workweek significantly, not about any particular way to do that. 

"Not every business can close their door on a Friday, it's just not practical. We didn't want customer service to go down, so we told staff that they needed to find a time that was appropriate to work for them," Lockhart recalls. 

Some companies may shutter for a whole day. Others may offer staff flexibility to schedule their allotted hours however they want. Wharton professor Adam Grant has even advocated for using reduced hours to shutter offices at 3pm

2. It doesn't have financial costs. 

Reporters, like everyone else, sometimes get carried away. They love a feel good story, know good news garners clicks, and generally like to keep things as simple as possible. All of which means that sometimes the news about yet another successful four-day workweek trial skews toward the benefits without being as upfront as it should about the costs. 

Because there often are costs. The recent Icelandic experiment added around $30 million to the government's budget, Lockhart notes. When one Swedish city ran a similar trial with care workers, staff costs rose 22 percent while employees were happier and more effective. 

That being said, not every organization that tries reducing hours ends up losing money due to the shift. When one Australian digital marketing agency gave its employees Wednesdays off, profits tripled for instance. The ratio of costs and benefits depends on the specific business, but don't assume cutting your workweek will automatically pay for itself.  

3. It will fix your culture problems.  

Will working fewer hours make your team less stressed and more productive? Just about every experiment I've ever read about says yes. But Lockhart cautions that doesn't mean four-day workweeks are a cure all for companies' cultural problems. If your office is dysfunctional before you trim employees' hours, it will likely be just as dysfunctional after. 

"If you have a culture of workplace bullying then you're going to have a culture of workplace bullying. If you have a culture of overwork then there's very different conversations to be had around how you'd change that," Lockhart tells Insider. 

None of which means that four-day workweeks aren't an intriguing idea that many trials suggest improve outcomes for companies and employees. But let's not be pie in the sky. No policy is all upside, simplicity, and sunny days. The idea may very well be worth considering for your company but you should go into the decision with open eyes about the complexities and trade offs.