The four-day work week has moved from management theory to lived policy across several countries. The evidence base is now large enough that HR leaders need a clear-eyed assessment — not hype in either direction. Here is what the research actually shows and what it means for companies in Bulgaria.
What the major pilots found
Iceland (2015–2019)
The Icelandic government and Reykjavík city council ran the largest trial of its kind at the time: 2,500 workers across public sector organisations shifted to a 35–36 hour week with no reduction in pay. The researchers from Alda and Autonomy concluded that productivity was maintained or improved in the vast majority of cases. Critically, worker wellbeing scores improved significantly. The trial was so successful that trade unions negotiated the right to reduced hours for 86% of Iceland's workforce in subsequent collective agreements.
United Kingdom (2022)
The 4 Day Week Global pilot involved 61 companies and approximately 2,900 employees. Companies committed to a 100-80-100 model: 100% of pay for 80% of time in exchange for 100% productivity. After the six-month trial, 92% of companies chose to continue the four-day week permanently. Revenue increased by an average of 35% during the trial period (though this also reflects post-pandemic recovery). Reported burnout fell by 57%.
Microsoft Japan (2019)
Microsoft Japan ran a compressed summer trial in August 2019. Productivity — measured by sales per employee — increased by 39.9%. Meeting time was cut, email communication increased in efficiency, and electricity consumption dropped by 23%.
Belgium and compressed weeks
In February 2022, Belgium became the first EU member state to legislate a right to the four-day week — but as a compressed model: employees can request to work their full statutory 38 hours across four days rather than five. This is not a reduction in hours; it is a change in how they are distributed. The law gives workers the right to request this arrangement; employers can refuse only with written justification.
What this means under Bulgarian law
Article 136 of the Bulgarian Labour Code defines the standard work week as five days with no more than eight hours per day — totalling 40 hours. A genuine reduction to 32–35 hours requires either a change to the employment contract or a new collective agreement. A compressed model (40 hours in four 10-hour days) is legally possible under Art. 136a, but requires employer–employee agreement and cannot exceed 10 hours per day. There is no legislation in force or currently under discussion in Bulgaria that would impose or incentivise a four-day week.
The practical HR question
For companies not waiting for legislation, the most important variable is role-level fit. The pilots that failed did so in roles requiring real-time coverage, shift handovers, or continuous client contact. The pilots that succeeded concentrated in knowledge work where deep focus produces better outputs than extended hours. Before designing a trial, HR teams need to segment their workforce by role type — and measure output, not presence.
