The world’s biggest trial of the four day work week has come to an end. These are the results 

This article has been updated. It was originally published on 21 June 2022.

Is the four-day work week a good idea, or is it unworkable for many industries – and even many people? The UK has been finding out in what’s been heralded as the biggest ever experiment based on this working model.

The majority of employers who took part in the project say they've seen productivity levels maintained, and improvements in staff retention and well-being. Business revenue stayed broadly the same, there was a 65% reduction in the number of sick days and 71% of employees reported lower levels of burnout.

The pilot project ran between June and December 2022 and was based on the 100-80-100 model: this means workers got 100% pay for working 80% of their previous hours in exchange for a commitment to maintain 100% productivity.

Of the 61 companies that took part, 56 say they will continue trying out the four-day week following the pilot, while 18 say they will make the change permanently.

Around 2,900 employees took part in the trial, in sectors from marketing and advertising, to finance, digital manufacturing and food retail. It was run by 4 Day Week Global in partnership with Autonomy, the 4 Day Week Campaign and researchers from the University of Cambridge and Boston College.

"This is a major breakthrough moment for the movement towards a four day work week. “Across a wide variety of different sectors of the economy, these incredible results show that the four-day week with no loss of pay really works," says Joe Ryle, Director of the 4 Day Week Campaign.

More than 80% of people in the UK would prefer a four-day work week, according to a survey in 2021 by recruitment company Reed. It lists the advantages of the four-day model as:

Improved morale and fewer absences: A shorter working week leads to less burnout, making staff happier and more focused in their roles.

Helps recruitment: Offering potential and existing employees a flexible working pattern will help attract and retain talented professionals.

However, there are also some potential disadvantages of the four-day work week, the recruitment agency says:

It doesn’t suit all industries: Some sectors require a seven-day-a-week presence, which could make a short working week impractical. Examples include emergency services, public transport networks and logistics.

It doesn’t suit all workers: Some employees prefer the structure of a five-day week, and some like working overtime.

It can increase costs: Some sectors, such as healthcare, require staff to work long shifts. Companies in these areas may have to pay more overtime or draft staff in to make any shortfalls.

Belgium: Belgian employees recently won the right to work a full week in four days without loss of salary. People will be able to decide whether to work four or five days a week.

New Zealand: Consumer goods giant Unilever says that following encouraging results from an 18-month pilot in New Zealand, it is expanding a four-day week trial to its business in Australia. "The New Zealand trial showed strong results against business targets, including revenue growth, with the vast majority of staff reporting feeling engaged, and absenteeism dropping 34%," the firm said.

Iceland: The country ran a four-day work week trial between 2015 and 2019. It found that the well-being of 2,500 workers who took part increased in terms of health and work-life balance.

Appetite for a more condensed work week also appears to be strong in the United States. A 2019 poll of 36,000 Americans carried out by YouGov America found that two-thirds of respondents would prefer a four-day work week – regardless of whether that meant longer working hours on those days.

The five-day week is often credited to Henry Ford, who in 1914 proposed that his car production switch from a six-day to a five-day rota. The creation of unions in the 20th century helped to make a five-day week and two days’ rest the norm.

Four-day work weeks became three times more common in the United States between 1973 and 2018, with an additional 8 million employees working such a pattern, according to research by the IZA Institute of Labor Economics. The rise wasn’t due to changes in demographics or industrial structures, but more a result of workers’ and employers’ preferences, the study notes.

The traditional nine-to-five, five-day work week “looks more old fashioned than a Ford Model T”, said global staffing company Manpower Group’s Chairman and CEO Jonas Prising, at the World Economic Forum’s annual meeting in Davos in May 2022.

All the signs point to an evolving definition of work, he added, flagging the need for companies to listen, learn and adapt to what employees want. He believes a four-day work week is the latest positive change in this area.