The Four-Day Workweek: What Five Years of Real-World Data Actually Show
After Iceland, the UK pilot, Spain's regional trials, and dozens of company-level experiments, the four-day workweek has more data behind it than any HR experiment of the decade. Here's what the data says.
The four-day workweek went from fringe to mainstream HR conversation around 2019. Six years later, the experimental data from Iceland (2015-2019), the UK pilot (2022), Spain's Valencia regional trial (2023), Belgium's legal codification (2022), and dozens of single-company pilots adds up to a real evidence base. The data is consistent enough to summarise.
What the major studies actually measured
- Iceland 2015-2019 — Reykjavík City Council and the Icelandic government ran two large trials covering 2,500+ workers, reducing hours from 40 to 35-36 with no pay change. Results published by Autonomy and Iceland's Alda in 2021 reported maintained or improved productivity and substantial wellbeing gains.
- UK pilot 2022 — 61 companies, 2,900 workers, 6 months, 100% pay for 80% of hours with 100% productivity maintained. Coordinated by the 4 Day Week Foundation, evaluated by Cambridge and Boston College. 92% of participating companies continued with the model after the pilot.
- Spain Valencia 2023 — regional government subsidised the move for 50 manufacturing and service firms; productivity and turnover data collected by the regional ministry.
The Eurofound publications database tracks the longer-term meta-analysis as it emerges.
The headline findings that replicate
Across the studies:
- Productivity is maintained or modestly improved in roughly 80% of organisations, dependent on baseline operating model
- Burnout and stress measures drop materially — typically 30-40% reduction in self-reported burnout
- Sickness absence falls modestly — around 10-15% reduction in some studies, larger in others
- Turnover drops sharply — the UK pilot reported a 57% reduction in resignations
- Recruitment improves — applications per role rise materially when the four-day model is mentioned
Where the model does not work cleanly
The data is less favourable in three operating contexts:
- 24/7 coverage roles — hospitality, healthcare, customer support, manufacturing shift work. The model requires either rotational scheduling (no actual hours reduction per worker) or additional hires (paying down the productivity gain).
- Heavy meeting/coordination cultures — the four-day model usually requires a meeting purge. Organisations that cannot reduce meeting load typically cannot reduce hours.
- Client-facing roles in five-day-week markets — works when the team rotates which day is off; fails when the client expectation is permanent five-day availability per named person.
The legal and practical preconditions
Most EU jurisdictions allow the move via individual contract amendment or works council agreement. The UK and US allow it under common-law contract variation. Belgium's 2022 legislation is the only national codification — it explicitly permits compressed-hours four-day schedules without reducing total hours, distinct from the productivity-pilot model.
For organisations evaluating, the 4 Day Week Foundation publishes a free implementation guide and ongoing pilot intake. See our hybrid work and total compensation glossary entries for the conceptual cross-references.