The 4-day week works – but only if you change the work

Is it really possible to give people an extra day off every week without sacrificing performance?

According to a new study in Nature Human Behaviour, yes – and it could also be one of the most effective ways to support employee wellbeing. The international trial, led by sociologist Wen Fan of Boston College and co-authored by Juliet Schor, Orla Kelly and Guolin Gu, found that moving to a four-day week with no reduction in pay  led to widespread improvements in workers’ mental and physical health, reduced burnout and increased job satisfaction.

The results span six countries – Australia, Canada, Ireland, New Zealand, the UK and the US – and involve 2,896 employees across 141 companies. Crucially, these organisations didn’t just shave a day off the calendar. Before the six-month trial began each company had around eight weeks to reorganise its operations. Meetings were streamlined and workflows were redesigned. The goal was to maintain productivity while cutting scheduled hours by 20%.

Twelve control companies that didn’t implement the change failed to see any of the positive outcomes.

So what can HR leaders take from this? Time, when thoughtfully managed, can be a strategic lever. But there’s more to this story than just adding ‘four-day week’ to your benefits package.

The efficiency dividend

At the heart of the trial’s success is a principle long understood but rarely enacted, that much of what fills the modern workweek is waste.

Researchers observed that companies in the trial achieved the same or similar levels of output by removing unproductive tasks – particularly unnecessary meetings – and by improving collaboration. These operational changes, not just the shorter week itself, helped preserve performance. 

And it’s a timely insight. Many organisations still struggle to define what “good productivity” looks like in knowledge work, especially in hybrid settings.

Pedro Gomes, an economist at Birkbeck University of London, notes in a write up in Nature magazine that rest and performance are not at odds. “When people are more well rested, they make fewer mistakes and work more intensely,” he tells the magazine. 

Indeed, participants in the study reported higher job satisfaction and fewer sleep problems – two metrics that rarely appear together in traditional workforce reporting but speak volumes about the lived experience of work.

Redesigning work, not just reducing hours

The research authors note: “Both company-level and individual-level reductions in hours are correlated with wellbeing gains, with larger individual-level (but not company-level) reductions associated with greater improvements in wellbeing.” In other words, how much a person’s own workweek changed had more impact than how much the organisation changed overall.

That matters for HR. It suggests that personal workload and control over time are key levers and not just headline policies. Giving someone a four-day week won’t have the intended effect if they still have to cram five days’ worth of meetings and outputs into four.

Wen Fan herself had anticipated this potential downside. “When workers want to deliver the same productivity, they might work very rapidly to get the job done and their wellbeing might actually worsen,” she told Nature. “But that’s not what we found.”

Instead, the opposite was true. The researchers identified three key factors mediating the wellbeing gains:

• Improved self-reported work ability
• Reduced fatigue
• Fewer sleep issues

These are all early warning signals of burnout and reversing them could be one of the most cost-effective forms of preventive health available to employers.

But what about productivity?

The trial didn’t formally assess company-wide productivity, though participating organisations were asked to maintain output levels. It’s a notable omission and one that critics will latch onto.

However, more than 90% of companies chose to continue with the four-day week after the trial ended, suggesting that perceived or actual productivity didn’t decline enough to warrant a return to the five-day model. 

It’s also worth noting that the benefits extended beyond the trial period. Data collected a full year after the initial intervention showed that employee wellbeing remained high, undercutting the idea that this was a novelty effect.

Mind the bias

As with any large-scale stud, context matters. All 141 companies volunteered to take part – meaning the sample may be skewed towards more progressive, change-ready organisations. The outcomes, therefore, might not translate directly to businesses with different cultures or operational constraints.

Moreover, all results were self-reported. That doesn’t mean they are invalid but it does open the door to social desirability bias – the possibility that participants exaggerated the benefits because they wanted to keep their extra day off.

The authors themselves call for further randomised studies to firm up the evidence base. But even with those caveats the direction of travel is clear. A growing body of research, from Iceland’s four-year public sector trial to UK pilots led by 4 Day Week Global, points to similar conclusions: reducing hours without cutting pay can work but only with intentional redesign.

Implications for HR

For people leaders the big takeaway isn’t that you should immediately shift to a four-day week but that wellbeing and performance are not in opposition and that time is a variable you can actively manage.

Here are four practical questions HR leaders should be asking:

1. Where are we wasting time?
   Audit meetings, workflows and reporting to identify what can be streamlined. Don’t reduce days without first reducing noise.
2. Do teams have autonomy over how they manage their time?
   Blanket policies rarely account for functional variation. Focus on outcomes and give teams permission to flex how they deliver them.
3. Are we measuring wellbeing in a way that informs action?
   Go beyond pulse surveys. Track indicators like sleep quality, fatigue and work ability – the early signs of burnout.
4. How could we pilot change in a low-risk way?
   Not every business can flip the switch overnight. Start with one team, one function or one month and iterate from there.

Citation: Fan, W., Schor, J.B., Kelly, O. et al. Work time reduction via a 4-day workweek finds improvements in workers’ well-being. Nat Hum Behav (2025)