Between June and December 2022, 61 companies in Britain, with around 2,900 staff between them, tried something most executives consider impossible: cut working hours and keep pay the same1,3.
There were only two conditions: pay stays at 100 percent, and the reduction in hours must be meaningful rather than a reshuffle. How to cut was up to each company: a full day off on Friday, staggered days between teams, or shorter days1.
The results, published in February 2023 by researchers from the University of Cambridge, Boston College and the think tank Autonomy, travelled the world attached to one number: 92 percent.
The numbers, and the one most often miscited
Of the 61 companies, 56 kept the four-day week after the trial ended, or 92 percent. Eighteen had already made it permanent by the time the report was published1.
The number of people leaving during the trial fell by 57 percent. On wellbeing, 39 percent of employees reported less stress and 71 percent reported lower burnout1.
Revenue is where care is needed. Among organisations able to supply data, revenue during the trial was essentially flat, up about 1.4 percent3. Compared with the equivalent period in earlier years, reported revenue was up around 35 percent1. The two figures measure different things, and the 35 percent does not show that a four-day week caused growth. Anyone quoting it to sell the idea upstairs is staking their credibility on a weak comparison.
A year later the researchers went back. At least 54 of the 61 organisations were still running it, and at least 31 had made it permanent policy2,4.
The limits, stated plainly
The trial was backed by a campaigning organisation, the companies volunteered, most were small knowledge-work firms, and much of the data was collected by the organisers. There was no control group in the strict sense.
That is not a reason to dismiss the results. A trial with self-selected participants still tells you what happens in places that want to try, and 61 organisations over six months is real data. It just needs reading at the right size: this is evidence that it can be done, not evidence that it works everywhere.
The part worth copying: how they prepared
For most Vietnamese employers a four-day week is not yet realistic, particularly in manufacturing, retail and shift-based services. But the way the trial was designed transfers to any large change in how work is organised.
Before starting, participating companies spent around two months preparing: reviewing processes to find work that could be dropped, cutting meetings, agreeing how shifts would be covered so customers saw no gap, and choosing in advance which measures they would track. Most of the productivity change came from removing unnecessary work, not from working faster.
That part applies even if you never remove a working day: an organisation forced to deliver the same output in fewer hours quickly discovers how many of its meetings were optional.
The risk nobody mentions: fewer hours, same work
There is a failure mode for the four-day week that does not show up in the 92 percent. It happens when an organisation removes a day but keeps the same workload, expectations and deadlines. People still deliver, by packing more into the remaining four days, answering messages on the day off and taking work home.
On paper every measure looks fine: output holds, staff say they like the new policy. What is actually happening is work intensification, and its consequences arrive late, as burnout and resignations, usually after six to twelve months.
In the better-run trials, most of the time saved came from dropping meetings, dropping reports nobody read and shortening approval chains. An organisation that cannot find things to drop is not ready to remove a day, and should stop at the process clean-up.
For manufacturers and shift-based services in Vietnam, the workable version is usually not four days. It is less routine overtime, stable rosters so workers know their schedule in advance, and making sure a day off is a day nobody calls.
