For a century the standard workweek has been treated as a fixed law of economic life: five days, roughly forty hours, everyone in at the same time. In the last few years that assumption has been quietly stress-tested. Dozens of companies and a handful of governments have run pilots of a shorter week with no cut in pay, and the results have started to pile up. In 2025 the largest study of the idea yet was published in a peer-reviewed journal, and in April that year Tokyo's metropolitan government began offering a four-day option to roughly 160,000 employees. What was a curiosity is now a small mountain of data.
So this is a good moment to ask the harder question: what do those pilots actually show? The honest answer requires keeping three distinctions in view throughout. First, results measured on a few dozen volunteer companies are not the same as an economy-wide effect. Second, workers feeling better is not the same as a firm performing better, and the two are measured very differently. Third, a report from the advocacy group that organized a trial is not the same as independent peer review. Hold those apart, and a nuanced picture emerges — genuinely encouraging on well-being, much thinner on hard output, and far from settled as policy.
Table of Contents
- What "100-80-100" actually means
- The evidence so far: what the pilots found
- Why it seems to work — and where the methods wobble
- The hard cases: where four days strains
- From experiment to policy
- What to watch
What "100-80-100" actually means
The model at the center of the current wave has a shorthand: 100-80-100. Employees keep 100% of their pay, work 80% of their previous hours — typically dropping from five days to four — and are expected to sustain 100% of their prior output. The framing was popularized by 4 Day Week Global, a non-profit that has organized many of the coordinated trials, on the premise that the lost day can be recovered through sharper focus and less wasted time [source: 4 Day Week Global, 2023].
It is worth pausing on what this is not, because the term "four-day week" hides two very different things. A genuine 100-80-100 week reduces total hours worked. A compressed week — the model Belgium wrote into law in 2022 — squeezes the same 38 or 40 hours into four longer days of roughly ten hours each, leaving total working time unchanged [source: Reuters, 2022]. The two produce different fatigue, different childcare logistics, and different economics. Most of the well-being findings below come from the reduced-hours version; conflating it with mere compression is one of the most common errors in the debate.
The evidence so far: what the pilots found
The UK trial and its follow-up
The best-known experiment is the UK pilot of 2022, run by 4 Day Week Global with the Autonomy Institute and researchers at the University of Cambridge and Boston College. From June to December, 61 companies and about 2,900 employees moved to a four-day week on full pay. When the organizers reported results, 56 of the 61 firms (92%) had chosen to continue and 18 had made the change permanent. Staff turnover fell 57% against the same period a year earlier, and 71% of employees reported reduced burnout [source: Autonomy, 2023].
Two caveats belong right next to those numbers. The companies volunteered, so they were probably predisposed to make it work, and the organizers are advocates for the policy — this is participant-reported data from an interested party, not a neutral audit. The widely repeated claim that revenue rose about 35% is especially soft: it compares the trial period to the same months a year earlier, a gap that could be explained by ordinary growth or market conditions rather than the schedule [source: Autonomy, 2023]. A follow-up a year later found the change durable: at least 54 of the 61 firms still had the four-day week in place and 31 had made it permanent, with the earlier well-being gains largely sustained [source: Autonomy, 2024].
The peer-reviewed study
The strongest evidence to date arrived in 2025, when researchers led by Boston College sociologists Wen Fan and Juliet Schor published in Nature Human Behaviour. Pooling 2,896 employees across 141 organizations in six countries — the US, UK, Ireland, Canada, Australia, and New Zealand — they compared surveys before and after a six-month four-day trial. Work-related burnout fell from 2.83 to 2.38 on a five-point scale, job satisfaction rose from 7.07 to 7.59 on a ten-point scale, and mental and physical health improved — changes not seen in a set of 12 control companies. The gains were driven partly by better sleep, less fatigue, and improved work ability [source: Nature Human Behaviour, 2025].
This is real peer-reviewed evidence, and it matters. But note carefully what it does and does not establish. Every one of those outcomes is self-reported well-being, gathered from survey questions such as how workers rate their own mental health. The study did not analyze company-wide productivity or revenue at all. And because the firms self-selected, the authors themselves flag the likely overestimate and explicitly call for randomized controlled trials to pin down the true effect [source: Nature Human Behaviour, 2025]. In other words, the best study we have is strong on how people feel and silent on how firms perform.
Germany and Portugal
Two 2024 government-adjacent trials add texture. In Germany, a nationwide pilot organized with the University of Münster ran 45 companies through six months; 73% chose to keep the schedule. Employees slept about 38 minutes more per week and were more physically active than a control group, and self-reported productivity rose. Tellingly, the researchers found no notable change in absenteeism or financial performance — well-being improved while hard performance held roughly steady rather than surging [source: University of Münster, 2024]. Portugal's government-backed trial, coordinated through Birkbeck and Henley Business School, ran about 41 companies who cut average hours from 41.6 to 36.5 per week. Exhaustion and negative mental-health symptoms fell against a control group, 93% of workers wanted to continue, and only four firms returned to five days [source: Henley Business School, 2024].
Why it seems to work — and where the methods wobble
The mechanism advocates propose is intuitive. Given one less day, teams cut the low-value parts of the week first: fewer and shorter meetings, less multitasking, tighter agendas. Better-rested workers concentrate more and burn out less, and the recovered focus offsets the lost hours. The consistent finding across pilots — that people report lower burnout and better sleep while output does not obviously fall — is at least consistent with that story.
But the methods have real limits, and they run in one direction. Companies that join these trials volunteer, which means the sample is tilted toward firms already confident it will work — classic self-selection that inflates apparent success. Most outcomes are self-reported, and employees who want to keep an extra day off have an obvious incentive to answer generously. Follow-up windows are short, samples are often a few dozen firms, and — crucially — hard productivity is rarely measured at all; the Nature team, with the largest dataset, did not measure it [source: Nature Human Behaviour, 2025]. The participating firms also skew heavily toward white-collar and knowledge work, where a wasted hour is easy to trim. None of this means the benefits are illusory. It means the evidence is strong for well-being, weak for output, and not yet the kind of randomized test that would let anyone generalize to the whole economy.
The hard cases: where four days strains
The pilots' composition is itself a warning. A software team can compress its week by killing meetings; a hospital ward, a factory line, or a fire station cannot. Where the work is continuous, shift-based, or face-to-face, the hours are the service, and cutting them means either hiring more people or covering less. Healthcare has to staff around the clock under safety and regulatory constraints; manufacturing depends on continuous production and expensive equipment utilization, so a shorter week can mean idle capital or an extra shift to arrange [source: APA Monitor, 2025]. There is a safety dimension too: compressing hours into longer days can raise fatigue in exactly the high-risk settings — construction, energy, transport — where tired workers are dangerous.
That does not make a four-day week impossible in these sectors; some hospitals and plants have experimented with rota redesigns. It does mean the headline results from knowledge-work pilots should not be read as a promise to a nurse or a machine operator. The cost question is also real and often skipped: if output per hour does not rise enough to cover the lost fifth day, someone — the employer, the customer, or the worker through slower raises — pays the difference. Fairly stated, the case for a four-day week is strongest where the bottleneck is attention, and weakest where the bottleneck is coverage.
From experiment to policy
Even with those caveats, the idea has begun crossing from corporate pilots into public policy — though "institution" still overstates it. Iceland is the most cited example: public-sector trials between 2015 and 2019 covering more than 2,500 workers led to agreements under which roughly 86% of the workforce gained shorter hours or the right to them [source: Autonomy, 2021]. But Iceland also illustrates the framing trap. Critics note the reduction was modest — often one to three hours, not a true four-day week — and that the "overwhelming success" headline rested partly on managers' own assessments, so the case is more measured than the slogans suggest [source: The Conversation, 2021].
Governments have taken different routes. Belgium legislated a right to request a compressed four-day week — same hours, four days — rather than a reduction [source: Reuters, 2022]. Spain went further toward the reduced-hours model, using EU-backed public funds to subsidize small and medium manufacturers that cut hours without cutting pay, a notable attempt to test the idea in industry rather than offices; a parallel experiment in Valencia found improved self-reported health [source: World Economic Forum, 2023]. And in Japan, where overwork is a chronic policy concern, the Tokyo metropolitan government began offering a four-day option to its employees in April 2025, explicitly linking it to work-life balance and the country's low birth rate, with other prefectures following [source: NBC News, 2025]. These are mostly public-sector or subsidized moves and opt-in rights, not economy-wide mandates — real momentum, but a long way from a settled norm.
What to watch
The four-day week has earned a serious hearing. Across independent settings, the well-being signal is consistent: less burnout, better sleep, high rates of firms choosing to continue. That is not nothing, and for knowledge-work employers competing for talent it may already be reason enough. What the evidence does not yet support is the stronger claim — that shorter hours reliably hold or raise output across the economy — because the studies that measure well-being mostly do not measure productivity, and the firms in them chose to be there.
So watch three things. First, randomized trials of the kind the Nature authors called for, which would separate the schedule's effect from the enthusiasm of volunteers. Second, results from outside the white-collar core — the manufacturing subsidies in Spain, any serious pilot in healthcare or continuous operations — because that is where the model's limits will show. Third, whether the government moves in Tokyo, Belgium, and elsewhere stay opt-in perks or harden into durable entitlements. Until then, the fair verdict is the careful one: a promising redesign of work with strong evidence for how it feels, thinner evidence for what it produces, and a real but unfinished path from experiment to institution.