The four-day week gets talked about as if it were a single thing, when really it is several. Cramming forty hours into four longer days is not what most advocates mean, and it tends to leave people frazzled. The version generating headlines is the 100-80-100 model, and the distinction matters more than any survey result.
What 100-80-100 actually means
The deal is simple to state and hard to deliver: 100 per cent of the pay, 80 per cent of the hours, in exchange for maintaining 100 per cent of the output. No salary cut, a day off, and the same results. The bet is that a five-day week is padded with low-value meetings, performative busyness, and interruptions, and that removing a day forces teams to cut the waste rather than the work. The UK 4 Day Week Campaign ran a large pilot in 2022 with dozens of organisations trialling it over six months, and most of the participating companies chose to keep the arrangement after the trial ended - which tells you more than any single statistic about how it felt from the inside.
Where it struggles
It is far easier in some jobs than others, and pretending otherwise is how pilots collapse. A software team or a marketing agency can ruthlessly delete meetings and protect deep-focus time. A hospital ward, a busy cafe, a call centre with a fixed volume of inbound calls cannot simply produce the same coverage in four days without hiring more people - and then the cost reappears.
- Coverage-based work - shift-driven, customer-facing, safety-critical - rarely fits the model cleanly.
- The hidden risk is intensification: if the fifth day's work just gets squeezed into four, you have traded a day off for four miserable ones.
- Some firms run a "fifth day" on rotation instead, so the business never fully closes - messier, but it keeps the doors open.
The trade-offs worth naming
For knowledge work where output is the measure rather than hours at a desk, a well-run four-day week is genuinely worth trialling, and a properly designed three-to-six month pilot with clear metrics is the sensible way to find out without betting the business on a hunch. What it is not is a free productivity hack you can announce on a Monday. It demands brutal honesty about which of your meetings deserve to exist, a willingness to let some lower-value work simply not happen, and managers who measure results rather than presence.
The companies that made it stick did not work the same way in four days. They stopped doing a chunk of what they used to do on the fifth - and discovered the world kept turning.