The five-day work week isn’t some natural law. It was a social convention established roughly a century ago, and there’s growing evidence that it might not be the best way to organise work anymore. The four-day work week has moved from fringe idea to serious policy discussion, backed by real data from real companies. Here’s what the evidence actually shows.

The Trials Tell an Interesting Story

The largest four-day work week trial to date was the UK pilot in 2022-2023, involving 61 companies and roughly 2,900 employees. The results were remarkably positive. Revenue stayed flat or increased at 95% of participating companies. Employee wellbeing improved significantly. And here’s the kicker: 92% of the companies decided to continue with the four-day week after the trial ended.

Iceland ran one of the earliest and largest trials between 2015 and 2019, covering about 1% of the working population. They found that productivity either maintained or improved in the majority of workplaces. Burnout dropped. Employee satisfaction rose.

Similar trials in Japan, New Zealand, Spain, and several other countries have produced broadly consistent results. The pattern is clear enough to take seriously: for many types of work, five days aren’t necessary to produce five days’ worth of output.

Why It Works (When It Works)

The explanation isn’t that people magically work faster. It’s that the traditional work week contains an enormous amount of waste.

Meetings shrink or disappear. When you have one fewer day, every meeting gets scrutinised. Is this necessary? Could it be an email? Could it be 15 minutes instead of an hour? Companies in four-day trials consistently report dramatic reductions in meeting time, and almost nobody misses the meetings that got cut.

Focus improves. Knowing you have less time creates a natural sense of urgency that reduces procrastination and encourages deeper focus. Parkinson’s Law — work expands to fill the time available — turns out to work in reverse too.

Energy levels stay higher. By Thursday afternoon in a five-day week, most people are running on fumes. Their Friday output is a fraction of their Monday output. With a three-day weekend to recover, people show up on Monday genuinely rested rather than still catching up from the previous week.

Retention improves. Companies offering a four-day week see significantly lower turnover. The cost of replacing an employee — recruiting, hiring, training — typically ranges from 50% to 200% of their annual salary. Keeping people happy enough to stay is an enormous financial advantage.

The Models

Not every four-day week works the same way. There are a few common approaches:

32 hours, same pay. This is the most common model in trials. Employees work four eight-hour days instead of five, with no reduction in salary. The bet is that productivity gains will offset the lost hours. In most trials, they do.

Compressed hours. Employees work the same 40 hours but spread across four days instead of five, meaning four ten-hour days. This preserves total working time but gives an extra day off. It’s simpler to implement but can lead to exhaustion — ten-hour days are long.

Alternating schedules. Some companies stagger which day each team takes off, ensuring five-day coverage while giving individuals a four-day week. This works well for customer-facing businesses that need daily availability.

Where It Doesn’t Work (Yet)

Four-day weeks work well for knowledge work — software development, marketing, consulting, design — where output is measured by quality rather than hours. They’re harder for continuous operations like factories and hospitals that need daily coverage, for client-facing roles where five-day availability is expected, and for early-stage startups where sheer intensity matters.

The Productivity and Well-Being Question

Does four-day productivity actually match five-day productivity? The honest answer: it depends. The UK trial showed stable self-reported productivity backed by revenue data, but self-reported productivity is notoriously unreliable. What we can say with confidence is that the relationship between hours and output isn’t linear. Beyond a certain threshold, additional hours produce diminishing returns.

Even if four-day weeks were completely productivity-neutral, the well-being benefits might justify them alone. Trial participants consistently report reduced stress, better sleep, and more time with family. An extra day per week also lets people handle medical appointments and errands without eating into weekends — removing a constant background stress.

What Would It Take?

Implementing a four-day week requires ruthless prioritisation (cutting meetings and low-value admin), trust from managers (micromanagement kills the benefits), outcome-based measurement (track what gets done, not hours at desks), and a willingness to experiment with a pilot before committing permanently.

The Bottom Line

The four-day work week isn’t a universal solution, and anyone who claims it works for every business is overselling it. But the evidence from multiple trials across multiple countries is compelling enough that every knowledge-work employer should at least be considering it.

The question isn’t really “can we afford to try a four-day week?” It’s increasingly “can we afford not to?”