Can a 4‑Day Workweek Boost Productivity? Inside the World’s Largest Trial

Global Largest Trial

From 6 May, a six‑month experiment in the UK involves more than 3,300 employees from 70 companies testing a four‑day workweek with an extra paid day and no salary reduction.

Participating firms say the pandemic prompted a rethink of work patterns, hoping to shorten hours without losing productivity while improving mental health and employee welfare.

Charity Bank CEO Ed Siegel argues that the five‑day model is outdated and that a four‑day week, with unchanged pay and benefits, will create happier teams and positively affect productivity, customer experience and social mission.

The trial spans finance, hospitality, care, catering, animation and other sectors, and will be monitored by researchers from Oxford, Cambridge and Boston College.

Researchers will record employee reactions to the extra day off, including stress, work‑life satisfaction, health, sleep, energy use and travel.

Results are expected in 2023 and will be submitted to the UK government to consider a 32‑hour workweek.

“100‑80‑100” Model

BBC headlines highlighted the model: employees keep 100 % of their salary while working only 80 % of the time.

The non‑profit 4 Day Week Global, which launched the initiative in 2021, promotes the “100‑80‑100” approach: 100 % pay for 80 % of work time in exchange for 100 % output.

CEO Joe O’Connor says companies are recognizing that improving employee quality of life gives them a competitive edge.

Research cited by the organization claims the four‑day week raises efficiency, cuts costs and boosts happiness—78 % of workers report feeling happier and less stressed, and 63 % of firms find talent attraction easier.

Economic forecasts suggest UK retail sales could rise by about £58 billion due to increased consumer spending on the extra day off.

A New Trend?

Other countries have experimented with shorter weeks. Iceland (2015‑2019) involved 2,500 public‑service workers, reporting reduced stress, higher happiness and a 25‑40 % productivity boost; now over 80 % of Icelandic employees work 35 hours weekly.

Microsoft Japan’s 2019 trial with 2,300 staff showed a 40 % productivity increase, better meeting efficiency, happier employees and savings in electricity and paper.

Critics warn that a shorter week may increase pressure on employees to complete the same workload, may be unrealistic for client‑facing or 24/7 services, and could raise overtime costs for employers.

A similar French trial found workers still needed five days to meet targets, leading to higher labor costs.

While the four‑day workweek challenges traditional models, widespread adoption will require further evidence and policy support.