You’ve heard about the 4-day workweek — but what about the 9-day fortnight?

You might have heard of the four-day workweek – where employees work just four of the traditional five working days, but for the same pay and with expectations of maintaining productivity levels.

A largely successful six-month trial of this working pattern recently ended in the U.K. Companies noted increased productivity and more interest from prospective employees, while workers say it improved their quality of life.

But concerns about factors like profit, added pressure for workers due to a higher daily workload and the need to be available to clients during all standard working hours remain.

Sam Franklin, the CEO of tech company Otta, adds that cutting a full day seemed like a big step as it cuts working hours by 20%.

“Going from effectively 100% of time to 80% of time I felt like potentially I was going to rock the boat too much,” he told CNBC Make It.  

So, is there a middle ground? Enter the nine-day fortnight.

The nine-day fortnight working pattern effectively means that across 14 calendar days, nine of them are working days and five are days off. Every other week, employees get an extra day off, often a Friday.

Some companies ask employees to work longer hours on the days they are working to allow for the extra day off, others say this is not important to them as long as their output remains consistent.

Otta is one of the many companies currently trialing this working pattern – with the view that if it goes well, a move to the four-day week could eventually be an option.

“As a stepping stone it felt like why wouldn’t you try nine day fortnights?” Franklin says.

Many of the benefits are similar to those of the four-day week, according to those who have tested it. This includes productivity, employee satisfaction, a better work-life balance and improved wellbeing. Franklin has also noticed the topic come up during the hiring process.

“It’s one of the things that everyone is mentioning. When they say ‘hey, why do you want to work at Otta?’ It’s ‘I read about this, I love the way you’re thinking, I’ve always wanted to do this.'”

Ben Branson-Gateley, CEO and co-founder of human resources software firm Charlie HR which also follows a nine-day fortnight, says he has noticed additional benefits compared to the four-day week.

“The reason why I’m really pro nine and not four is Thursday doesn’t become the new Friday,” he says. Alternating four and five-day weeks also creates a better balance, Branson-Gateley has found.

“Those four day weeks, they can feel a lot, they can feel quite intense,” he says. “I don’t love the idea of doing that every week.”

Employees are able to switch between working styles and can adapt to how they work based on how many days their working week has, as well as enjoying quality of life improvements, Branson-Gateley explains.

Both Branson-Gateley and Franklin have seen their employees change the way they approach work as a consequence of the nine-day fortnight. Franklin encouraged his employees to question whether work meetings that don’t relate to decision-making or relationship building are really necessary, while Charlie HR has implemented a (mostly) meeting free “deep work Wednesday.”

Much like the four-day week however, the nine-day fortnight doesn’t suit every business and every employee. Public relations firm Stand, who are based in London, is one of them, founder Laura Oliphant explains.

“The benefits were obvious, I felt we were better supporting employee’s mental wellbeing, reducing stress and burnout, allowing for time to switch off. And the team felt more productive. But there were some drawbacks,” she explains.

Not all workers noticed the benefits, Oliphant says, and because clients needed to be able to reach someone at the firm any day, Stand had to set up a rota, giving individual employees different days off.

“The rolling rota was time consuming and complex to develop, everyone was working towards different timelines, [and] teams were strained when the rota coincided with busy holiday periods,” Oliphant says.

Stand now follows a 4.5 day working pattern – on Fridays everyone signs off at 1 p.m., bar one person per team who keeps an eye out for important emails.

This has addressed the issues the firm found with the nine-day week, but the benefits have remained. And Oliphant’s biggest lesson from the experience?

“A key takeaway for us is not to be restricted by a flexible model that works for someone else. It’s important to find one that’s right for your business and your clients,” she says.