The Four-Day Week Trials Are Over. Here Is What Every One Of Them Found
Co-Founder and Chief Data Scientist
The Nature Human Behaviour study, published online on July 21, 2025, analyzed pre-trial and post-trial data from 2,896 employees at 141 organizations in Australia, Canada, Ireland, New Zealand, the United Kingdom and the United States after a six-month trial that cut the working week to four days with no reduction in pay. Boston College and University College Dublin researchers found that participants reported lower burnout, higher job satisfaction and improved self-reported mental and physical health, a pattern not observed at 12 control companies.
The headline result requires an important qualification. None of the trials established that every workplace can remove a full paid day without additional costs, and the strongest benefits went to employees whose working hours genuinely declined.
Actual Hour Reductions Drove Stronger Benefits
In the six-country study, employees who reduced their own hours more experienced larger well-being improvements, although larger reductions measured at the company level did not have the same relationship. Improved self-reported work ability, fewer sleep problems and reduced fatigue mediated the gains, the research team reported.
Organizations also reorganized work before cutting hours, seeking greater efficiency and collaboration. The intervention therefore tested redesigned processes alongside reduced schedules, while Boston College’s Schiller Institute characterized the well-being evidence as strong and the organizational-performance evidence as only “moderately good.”
Britain Paired Human Gains With Limited Financial Data
The University of Cambridge, working with Boston College and Autonomy, evaluated a June-to-December 2022 pilot in which 61 organizations employing about 2,900 people were asked to reduce working time by 20% without cutting pay.
In the Cambridge team’s February 2023 results, 71% of employees reported less burnout and 39% reported less stress than when the trial began. The evaluation also found a 65% reduction in sick days and a 57% decline in employees leaving participating organizations compared with the equivalent period one year earlier.
Among the 23 organizations that supplied usable revenue figures, average revenue increased by 1.4% during the trial, although that subset represented fewer than two-fifths of participating employers. The Cambridge team reported that 56 of 61 organizations intended to continue the shorter week, with 18 confirming at that point that it would become permanent.
However, a 2025 peer-reviewed analysis in Humanities and Social Sciences Communications, drawing on the pilot report, found that average weekly working time fell by approximately four hours, considerably less than a full 20% reduction.
Portugal Repeated The Pattern With A Smaller Cut
Portugal’s government-backed program included 41 companies that shortened their working weeks, with 21 coordinating the start of a six-month pilot in June 2023, the 4 Day Week Global public summary reported. Birkbeck, University of London, and Henley Business School jointly conducted the research.
During the first three months, more than 1,000 employees reduced their working time by 13.7%, rather than 20%. The pilot’s own public summary reported that work exhaustion declined by 19% and that the proportion struggling to reconcile work and personal life fell from 46% to 8%; its final public summary also said that 95% of participating companies evaluated the trial positively.
Iceland Maintained Services Through Operational Changes
Reykjavík and Iceland’s national government conducted two trials between 2015 and 2019 involving more than 2,500 public employees, or more than 1% of the country’s workforce, according to the Iceland trial report from Autonomy and Iceland’s Association for Sustainable Democracy. Many participants moved from 40 hours to 35 or 36 hours without reduced pay.
Across offices, schools, social-service providers, police operations and hospital departments, the report found that productivity and service provision remained unchanged or improved in most workplaces, while perceived stress, burnout, health and work-life balance generally improved. Maintaining services required shorter meetings, altered schedules, revised opening hours and fewer informal interruptions; where those efficiencies were insufficient, some workplaces hired additional employees.
Productivity Evidence Remains Less Certain
A Eurofound literature review, prepared for a European Commission pilot project and concluded in 2024, found that reduced working time was positively associated with worker health and well-being, while effects on productivity, employment and the environment remained more uncertain. Information technology and business services were also more heavily represented than industrial work in the studies covered by the Eurofound review.
The review noted that Scandinavian shorter-day experiments in health and social services generally used control groups, while four-day reduced-hours evaluations frequently did not, and recommended longer follow-up periods and more comparison groups. A separate 2024 systematic review by University of Northampton researcher Timothy Campbell examined 31 academic articles spanning more than five decades and found productivity evidence inconclusive, despite frequently favorable outcomes for morale, job satisfaction, turnover or costs.
Eurofound also found more mixed results when employees compressed the same weekly hours into four longer days. Employers and workers assessing a proposal should therefore determine whether paid hours will genuinely fall, whether staffing can still meet demand and whether unnecessary work will be removed. Success requires service and output measures alongside employee surveys, because the evidence is strongest when shorter schedules reflect less time working rather than a rearranged calendar.
