The Four Day Work Week Experiment Nobody's Talking About

Eighteen months after 34 UK companies committed to a permanent four-day work week for 2,100 employees, the group behind the trial, 4 Day Week UK, published results on September 3 showing employee turnover fell 37 percent compared with each company's prior 18-month period, while self-reported productivity held roughly flat.

This is a quieter story than the original 2022 pilot that made headlines, because it tracks what happened after companies made the schedule permanent rather than testing it for six months. Permanence changes behavior in ways a short trial cannot capture.

What actually changed

Not every company kept the exact same structure. 28 of the 34 companies used a compressed model, four eight-hour days, while six used a reduced-hours model, four six-hour days at full pay. Turnover improvements were similar across both models, though the sample size for the six-hour group is small enough that the researchers flagged it as preliminary.

The companies span professional services, marketing, and software, industries where output is easier to measure by results than by hours at a desk. None of the 34 companies were in manufacturing, retail, or healthcare, sectors where a four-day week is structurally harder to implement.

“The productivity number is almost beside the point after 18 months. The number that made every one of these companies decide to keep the policy was turnover, because replacing an employee costs six to nine months of their salary in most estimates, and a three-day weekend costs nothing.”

What this does not prove

The study is not a randomized controlled trial. Companies volunteered to participate, which means the group likely already had cultures more receptive to the change, and the results may not generalize to industries or companies that would need more convincing. The researchers themselves describe the findings as strong observational evidence, not conclusive proof of causation.

Still, an 18-month permanent trial with a 37 percent turnover drop is a different kind of evidence than a six-month pilot, and it is likely to shape how the next round of companies, particularly in the US, where a four-day week remains rare, think about the tradeoff between hours worked and hours needed to keep an employee at all.