In any given workday, how much time you think you actually spend working? By some accounts, it's only three hours a day.

When Andrew Barnes, the founder of a New Zealand-based trust planning firm Perpetual Guardian heard this, it gave him an idea. What would happen if he gave his 240 employees every Friday off for two months? He wondered if staff would work smarter if they were given a personal day every week.

Employees maintained the same working hours Monday through Thursday, and they got paid exactly the same as before. Barnes says he believes he's the first company that has paid employees for five days of work when they only worked four.

New York Times wrote about Perpetual Guardian's experiment with the 4-day workweek, and the results are resoundingly clear: It was an overwhelming success. Employees got the same amount of work done in 32 hours that had previously taken 40. They were paid the same.

Barnes also hired a couple researchers to study the effects on employees and their productivity. They uncovered some pretty salient findings. One researcher said people felt more creative, attendance and punctuality improved, and people didn't leave early or take unnecessarily long breaks. The case for the 4-day workweek is so compelling that Perpetual Guardia is now considering making it permanent.

Here's what happened when employees got every Friday off for two months.

Job performance stayed the same

Employees were more productive when they had fewer days to work. Even though the entire company lost a full nine days of work over the two months, job performance remained the same.

This made Barnes realize that employees should not be judged based on how much time they spend in the office. You shouldn't get bonus points just for being there. He believes employees should be compensated based on performance. He says: "If you deliver that in less time, why should I cut your pay?"

Everyone simply felt better

Staff reported a 24 percent improvement in work-life balance. Because they had an extra day for leisure activities and spending time with their families, employees were more energized when they came back to work the following week.

One such employee is Tammy Barker, who has two children. She told New York Times that she spent her day off running errands and grocery shopping. She was then able to spend time with her family on the weekends.

Efficiency and productivity skyrocketed

With a full eight hours slashed from their workweek, Perpetual Guardian employees learned to be more efficient with less time. Staff said they were motivated to be more productive at work.

They stopped wasting so much time in meetings. Two-hour meetings became 30-minute meetings. Staff also created signals to let each other know when they needed to put their heads down and focus. This would let other people know they didn't want to be bothered.

Tammy Barker, the employee interviewed by New York Times, said she learned to mono-task instead of multi-tasking. Instead of trying to do several things at once or jump between tasks, she practiced finishing what she started before moving onto something else. It made her vastly more productive. "At the end of each day, I felt I had got a lot more done."

Other organizations have experimented with paid personal time off. Many companies reward employees with paid sabbaticals. E-commerce and marketing company Weebly offers six-week paid sabbaticals after employees have worked there for five years. Global aviation strategy company SimpliFlying made it mandatory for employees to take one week off every seven weeks. Most report good results, both for employee productivity and retention.

If you work hard to keep employees happy and invest in them enjoying their lives outside of work, they'll probably be more motivated on the job.