Four Years of Four-Day Weeks: What the Long-Term Data Actually Says

The four-day week has been the most argued-about idea in work culture for a decade. The argument finally has something it lacked: data. Not LinkedIn anecdotes or CEO opinion pieces — real trials, at real companies, measured by researchers and published in peer-reviewed journals.

The headline numbers

The largest trial started in June 2022: 61 British companies, about 2,900 employees, six months on the "100:80:100" model — 100% of pay, 80% of the time, 100% of the output. The skeptical prediction was a productivity cliff. It didn't appear. Revenue rose 1.4% on average during the trial; burnout fell 71%; stress fell 39%; sick days dropped 65%; resignations dropped 57%. Fifteen percent of employees said no amount of money would convince them to return to a five-day week.

Then came the harder test: did it last? At the end of the pilot, 56 of the 61 companies chose to continue. A year later, 54 were still running it, and 31 had made the change permanent. "Real and long lasting," said Boston College's Juliet Schor, who led the research alongside Cambridge's Brendan Burchell. Burchell put the core finding plainly: "Before the trial, many questioned whether we would see an increase in productivity to offset the reduction in working time — but this is exactly what we found."

A second, smaller British trial — 17 companies, roughly 1,000 employees, run from November to April and evaluated by Boston College researchers — ended with all 17 adopting the model permanently. Twelve took the straight four-day week; five chose a nine-day fortnight. Burnout fell 62%, mental-health ratings improved 41%, life satisfaction rose 45%, and one software company, Brandpipe, reported a 129% revenue jump.

But the most rigorous data comes from the long-term report by 4 Day Week Global, covering firms in the US, Canada, Britain and Ireland, published in Nature Human Behaviour. Comparing baseline to 12 months after launch: burnout down 69%, self-reported work ability up 57%, attrition down 32%, revenue up 15%. Employees, on average, cut about four hours off their week in the first six months — and those who stayed on the schedule a full year shaved off another hour. Ninety-five percent wanted to keep it.

Here's a detail worth lingering on: well-being gains scaled with how many hours people actually cut. The 33-hour-week crowd improved more than the 38-hour crowd. That's important, because it points at the mechanism — it's the rest doing the work, not the novelty of being watched.

The country that went first

Before Britain, there was Iceland. Between 2015 and 2019, about 2,500 public-sector workers — preschool teachers, nurses, hospital staff, social workers, city office employees, just over 1% of the country's workforce — cut their week from 40 hours to 35 or 36, with no pay cut. The research, run by the UK think tank Autonomy and Iceland's Alda, found productivity held steady or improved in most workplaces: 86% of participants reported less stress, 71% reported less burnout, and over 90% preferred the shorter week.

What happened next is the part other countries keep skipping. Iceland didn't pass a law mandating four-day weeks. Its unions negotiated reduced hours into collective agreements across the labor market. By 2025, roughly 86% of Iceland's workforce had shorter hours or the contractual right to them — the closest any country has come to universal adoption. And the economy didn't sputter: Iceland's GDP grew 5% in 2023, outpacing most European peers, with unemployment at 3.4%. One unexpected dividend: men took on more housework, narrowing the domestic labor gap.

The one that broke

Not every trial is a fairy tale, and the failures are more instructive than the successes. Safeguard Global, a Texas-based workforce management company, started testing a four-day schedule in 2023 with about 20 engineers spread across 26 countries. The idea was to attract and retain talent.

At first, people liked it. Over time, the work seeped back in. Some employees compressed five days of work into four longer ones and burned out anyway. Others quietly kept working on Fridays. The people who did protect Friday worried they were falling behind — which replaced one kind of stress with another. Managers ended up reminding people to log off. CEO Bjorn Reynolds eventually dropped the fixed schedule entirely in favor of individual choice backed by outcome-based measures. Today, the company's roughly 1,000 remote employees across 78 countries pick their own pattern.

The diagnosis from Inc.'s Scott Hutcheson is the sharpest sentence written about this whole movement: the organization changed the container without changing what employees were expected to fit inside it.

The policy isn't the intervention

That's the rule that separates the trials that worked from the one that didn't. In the UK and Iceland trials, companies didn't just delete Friday — they redesigned the work. Meetings got culled. Standing meetings got shorter agendas or died entirely. Simultaneous priorities were cut. Coverage plans were written down: who answers the customer when the team is off. Response-time expectations were renegotiated. Decision rights were clarified so people didn't spend Thursdays waiting for approvals that wouldn't come until Monday.

The 100:80:100 model only balances if the "100% of output" is redefined rather than compressed. Keep every deadline, every meeting, every expectation, and you don't get a four-day week — you get secret Fridays.

A note of honesty before the cheerleading: the researchers are upfront about the caveats. The participating companies volunteered, and volunteers are not a random sample — firms that signed up probably already believed it could work for them. There was no large randomized control group. The surveys are self-reported. And almost all the trials were in high-income, English-speaking countries, at companies small enough to be flexible. "We should be careful in making sweeping claims," said researcher Wen Fan, whose team also checked for the Hawthorne effect — people performing better simply because they're being studied. The sustained 12-month results argue against pure novelty, but they don't prove the model works for a 50,000-person factory or an emergency room.

What to do with this

If you run a company and the numbers tempt you: the data says the risk is in the implementation, not the calendar. Run it as a six-month pilot, but budget the redesign time — audit your meetings, kill the standing ones, write the coverage rota, and watch for the secret-Friday signals: messages landing on the protected day, creeping hours, employees hitting targets only by hiding extra effort.

If you're an employee hoping your employer tries it: the leverage is real. Across the global trials, 63% to 83% of companies reported that hiring and retention got easier, and one Australian firm saw job applications jump 600% after switching. But negotiate for fewer hours, not just fewer days. The trials that produced the gains weren't about four brutal 10-hour days — the well-being improvements tracked with actual hours cut. Four days of 10 hours is not a shorter week. It's the same week, rearranged.

Four years of data haven't ended the argument, but they've changed it. The question isn't whether people can do good work in fewer hours — thousands of trials say they can. The question is whether your organization is willing to change how it works, not just when.

References

• 4 Day Week Global — Long-Term Pilot Report (12-month data)
• PsyPost — Large-scale trial findings (Nature Human Behaviour)
• SpaceDaily — UK trial: 56 of 61 firms stayed, burnout fell 71%
• People Management — 17-company UK trial: all adopted permanently
• MedBound Times — Iceland's 4-day workweek: six years on
• Financial News — The country that measured everything
• Inc. — A company tried a 4-day workweek; employees secretly worked Fridays
• The US Leaders — Four-day work week: real results from real companies