Ask finance directors what a four-day week must prove and they usually reach for productivity. The pilots suggest a different first place to look: the cost of people leaving, roles sitting empty, and agency staff filling gaps. Retention is where a shorter week pays earliest and most measurably.
What the pilots saw
In the UK 2022 pilot, the number of staff leaving fell by 57% during the trial compared with a comparison period — a large percentage on a small base, so read it as direction rather than destiny. In the US and Ireland pilots, 97% of employees wanted to continue working four days, and companies rated the experience around 9 out of 10. People who have had a real day back do not volunteer to return it.
Iceland’s public-sector experience points the same way at national scale: after trials involving 2,500 workers showed productivity maintained and wellbeing improved, around 86% of Iceland’s workforce moved to shorter hours or gained the right to them. Arrangements that staff experience as a loss when threatened do not spread like that.
Do the arithmetic for your organisation
Most firms already know these numbers; they just never sit them next to the four-day week proposal. Take your last twelve months: how many leavers, in which roles, at what replacement cost? Common estimates put the cost of replacing a skilled employee at a substantial fraction of annual salary once recruitment, onboarding and lost productivity are counted. Add vacancy costs — overtime, agency spend, delayed projects, the manager hours spent interviewing — and hard-to-fill roles where a vacancy runs for months.
Now ask a narrower question than “will productivity rise 20%?” Ask: “If a credible shorter week cut regretted leaving in scarce roles by even a modest amount, what would that be worth?” For many employers in 2023’s tight labour market, that answer alone clears the bar for a pilot. You do not need heroic productivity assumptions; you need fewer resignations in the three teams you cannot afford to lose.
Retention only counts if the hours really fall
Staff are not retained by a policy label. They are retained by Wednesdays that are actually off, Fridays that stay quiet, and workloads that were genuinely redesigned. If your pilot keeps five days of work and compresses it, expect intensity complaints and the retention benefit to evaporate. The UK pilot’s average hours fell from about 38 to 34 a week; that felt reduction is the product people are loyal to.
This also means protecting the benefit during busy periods. A day off that disappears every time a deadline looms teaches staff that the promise is conditional. Agree peak-period rules in advance — how cover works, what gets deprioritised — rather than quietly borrowing the day back.
Equity is a retention issue
Nothing corrodes a retention story faster than a two-tier workforce: office staff on four days, frontline or part-time staff watching from the old rota. If full-time hours fall from 40 to 32 at the same pay, part-time colleagues’ hourly rates usually need a pro-rata uplift. Where an identical model genuinely cannot work for a coverage role, offer equivalent value — additional leave, a nine-day fortnight, shift premiums — and say so plainly.
Track leaving by group during the pilot, not just firm-wide. If your headline retention improves while one team churns, you have not built a retention policy; you have built a perk for the already comfortable.
Make it a board number
Put three figures in your pilot scorecard: resignations per month by team, time-to-fill and agency spend on hard-to-fill roles, and offer-acceptance rate. Baseline them, review them with the same seriousness as revenue, and publish the follow-up. Of all the claims made for the four-day week, “good people stay” is the one your own data can confirm fastest.
Sources
- Autonomy, University of Cambridge, Boston College and 4 Day Week Global, UK pilot results, February 2023: https://www.sciencedaily.com/releases/2023/02/230221113132.htm
- 4 Day Week Global, US, Ireland and international pilot results, December 2022: https://www.internationalworkplace.com/community-zone/news/four-day-week-pioneering-pilot-program-a-huge-success-new-research-reveals
- Autonomy and Alda, Iceland trials, 2021: https://phys.org/news/2021-07-shorter-week-boost-productivity-burnout.html
Day5Group is a consultancy that assists in the transition to a 4 day work week. More about Day5Group · All blog articles