An original TeaLamp explainer based on the sources listed below. Prepared by the TeaLamp Editorial Team with the help of AI.
For most of modern working life, five days on and two days off has felt like a law of nature. It is not. It is a schedule built for factory work a century ago, and in the last few years it has been put to a serious test. From Iceland to Germany, thousands of workers have tried a four-day week at full pay. The results are encouraging, and more complicated than the headlines suggest.
Key takeaways on four-day week
- The usual deal is called 100-80-100: 100 percent of the pay, 80 percent of the hours, and 100 percent of the output.
- Iceland tried it first, from 2015 to 2019, with more than 2,500 public workers. Productivity held steady or improved, and about 86 percent of the country’s workforce now has shorter hours or the right to ask for them.
- Britain’s 2022 pilot, with 61 companies and about 2,900 workers, found burnout down for 71 percent of staff and sick days down 65 percent, but the firms volunteered and there was no control group.
- A 2025 study in Nature Human Behaviour, covering 141 organisations with a comparison group, found gains in wellbeing that were still there a year later.
- Germany’s 2024 trial kept 73 percent of its 45 companies on shorter hours, and Portugal’s kept most of its firms too, though not all of them.
- The evidence is strongest on wellbeing. It is thinnest on productivity, which no big trial has measured directly.
The deal: same pay, fewer hours
The model behind almost every trial has a simple name: 100-80-100. Workers keep 100 percent of their pay, work 80 percent of their old hours, and commit to delivering 100 percent of their usual output. In practice that usually means a 32-hour week instead of 40, with Fridays off, or teams rotating their day off.
The five-day week was itself an experiment once: Henry Ford moved his factories to five days in 1926. Working time has been renegotiated before, and this time researchers are watching.
Iceland tried it first
The longest-running test began in Iceland in 2015, when Reykjavik City Council and the Icelandic government moved more than 2,500 public workers, about 1 percent of the country’s workforce, from a 40-hour week to a 35- or 36-hour week at the same pay. The think tank Autonomy and Iceland’s Association for Sustainable Democracy published the results in 2021, after the trials ended in 2019.
The findings were strikingly calm. Productivity stayed the same or improved in most participating workplaces, burnout and stress fell, and sick days dropped modestly. Overtime did not rise to fill the gap: workers finished the same work in fewer hours, often by cutting meetings. Then came the part that made Iceland different from every trial since. The unions used the results as a bargaining template, and in contracts negotiated between 2019 and 2021 they won permanent shorter hours for tens of thousands of members. About 86 percent of Iceland’s workforce now works shorter hours or has the right to ask for them. There was no four-day-week law. The change came through collective agreements, one sector at a time.
Britain’s big test
The best-known trial ran in Britain from June to December 2022. Sixty-one organisations and about 2,900 workers took part, organised by 4 Day Week Global and the think tank Autonomy, and studied by researchers at Cambridge and Boston College. The report, published in February 2023, explains the headlines: 71 percent of employees said their burnout had fallen, 39 percent felt less stressed, sick days fell by 65 percent, and resignations fell by 57 percent compared with the same period a year earlier. Revenue stayed broadly the same, rising 1.4 percent on average among the firms that shared financial data. Fifty-six of the 61 companies, 92 percent, kept the four-day week, and 18 made it permanent.
Those numbers deserve their honest footnotes. Every company volunteered through an advocacy organisation, so the sample is made of firms that already wanted the idea to work. There was no control group. The sick-day and resignation figures come from company records covering small numbers of people, and the researchers say the samples are too small to call the changes statistically significant. Only 23 of the 61 firms shared revenue data. A second, larger revenue number sometimes quoted from the same report, a 35 percent rise, compares the trial months with the same months a year earlier, mixing the shorter week with ordinary business growth. A year later, though, the results had sticking power: a follow-up in February 2024 found that 54 of the 61 companies were still on shorter hours, and 31 had made the change permanent.
The study with a control group
The fairest criticism of the British trial was that it had no control group, and in 2025 the evidence grew stronger. Wen Fan, Juliet Schor and colleagues published a study in Nature Human Behaviour pooling six-month trials at 141 organisations in six countries, covering 2,896 employees. Twelve companies that had shown interest in a four-day week but kept five days served as a comparison group. Average weekly hours fell from about 39 to about 34. Burnout fell from 2.83 to 2.38 on a five-point scale, and job satisfaction, mental health and physical health all improved. The comparison companies showed no such change. The gains were still there when the trial firms were checked again a year later.
The authors are open about the limits. The companies volunteered rather than being randomly chosen, all the outcomes were self-reported, and the sample leans toward smaller firms in English-speaking countries, mostly professional services and non-profits. The study is the strongest evidence yet that shorter hours improve how workers feel. It still does not measure output per hour, which no large trial has done directly.
Germany and Portugal: the idea travels
The trials kept spreading. In Germany, 45 companies from 13 industries ran a six-month trial in 2024, organised by 4 Day Week Global, the University of Münster and the consultancy Intraprenör. When it ended, 73 percent of the companies decided not to go back to five days, 20 percent returned, and 7 percent were undecided. Resignations fell 42 percent, burnout fell 64 percent, and companies cut their meeting load by 60 percent. More than 90 percent of employees said their wellbeing had improved, and they slept an extra 38 minutes a week. Two companies dropped out early, citing economic difficulties unrelated to the shorter week. Two years on, 70 percent of the organisations were still on some form of reduced hours.
Portugal ran a government-backed pilot in 2023 with 41 companies and more than 1,000 workers. Weekly hours fell by almost 14 percent, from 39.3 to 34. Of the 21 companies that started together in June 2023, twelve continued, five scaled the shorter week down, and four went back to five days. That split is worth remembering: the four-day week is not a result every company keeps.
A plant and a cup of tea on an office windowsill. Image generated by AI.
What the trials did not prove
Read together, the trials support a narrower claim than the headlines suggest. They show, fairly reliably, that workers feel better on shorter hours: less burned out, less stressed, sleeping a little more, and less likely to leave. Most participating companies keep the arrangement, which is a real vote of confidence from the people paying the wages. What they do not show is that a four-day week makes each hour more productive. Revenue held steady in the firms that reported it, but revenue is not output per hour, and fewer than half the firms in the British trial shared their figures at all.
There are also jobs the trials barely touched. The participating companies were mostly small and white-collar: offices, studios, charities and professional services. A hospital ward, a school, a factory line and a shop floor cannot simply close on Fridays, and the trials say little about shorter hours where cover matters most. Iceland’s public-sector trial is the exception, and even there the change was negotiated workplace by workplace.
None of this makes the four-day week a failure. It makes it a specific tool with specific evidence: strong for wellbeing, promising for retention, unproven for productivity, and dependent on how carefully a workplace redesigns its week. A company that copies the schedule without copying the redesign, cutting meetings, rethinking cover and trusting staff to finish the work, is copying the wrong half of the experiment.
A quiet park bench on a weekday afternoon. Image generated by AI.
Frequently asked questions
Does a four-day week mean a pay cut?
Not in these trials. The model is 100-80-100: the same pay for 80 percent of the hours. Belgium’s 2022 reform is different: it gave workers the right to ask for their full weekly hours squeezed into four days, a compressed week, not a shorter one.
Would a four-day week work in every job?
No. The trials were mostly office and professional work. Jobs that need fixed cover, such as hospitals, schools and shops, need a different design, for example staggered days off so the service never closes. Iceland’s trial worked because each workplace redesigned its own rota.
Is any country making the four-day week law?
No country has a general four-day-week law. Belgium gives workers the right to request compressed hours, and Iceland’s shorter hours came through union contracts rather than a statute.
Why it matters
The four-day week matters because it tests an assumption most of us never question: that five days is the natural shape of work. The trials suggest the shape is negotiable, and can leave both sides better off. But they also show that the schedule alone does nothing. The companies that kept it changed how work was done, not just when. That is the part worth copying: fewer meetings, clearer priorities, and trust that adults can finish the job. The extra day off is the reward for that redesign, not a substitute for it.
Related reading
For another story about how small businesses actually fare, read Business Survival Rates: How Long Do New Businesses Last?
Sources
- Autonomy, “The results are in: The UK’s four-day week pilot,” February 2023
- Fan, Schor, Kelly and Gu, “Work time reduction via a 4-day workweek finds improvements in workers’ well-being,” Nature Human Behaviour, July 2025
- 4 Day Week Global, “Germany Four-Day Workweek Pilot Results,” 2024
- Autonomy and Alda, “Going Public: Iceland’s journey to a shorter working week,” June 2021
- “4-Day Work Week Statistics 2026: Trial Results & Surveys,” October 2026 (Portugal pilot and one-year UK follow-up figures)
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