Four-day week pilots produce irresistible charts. Sick days down 65%. Staff leaving down 57%. Revenue up. A consultancy that wants to be trusted has to explain what those numbers are made of — because the same chart-reading discipline you apply to pilot headlines is the discipline you will need in your own boardroom.
Small bases make big percentages
The UK 2022 pilot reported sick and personal days down 65% and staff leaving down 57% against comparison periods. Both moves are welcome. Both rest on small denominators: in one summary, sick and personal time fell from about 2.0 to 0.7 days per employee-month. In a workforce of thousands that is meaningful; in a single firm of twenty, a handful of people’s health or decisions can swing the percentage wildly.
The rule is simple: never quote a pilot percentage without its base. Ask “down from what, to what, across how many people, over what period?” If a vendor cannot answer, treat the number as marketing.
Who is in the denominator?
Revenue in the UK pilot rose 1.4% during the trial across firms that reported it. In the US and Ireland pilots it rose about 8.1%. Those denominators matter. Not every firm reports revenue; growing firms volunteer for pilots; and a six-month window captures market weather as well as working-time effects. The UK also reported a much larger rise against a similar prior period — a figure that likely says as much about firm growth and survivor bias as about Fridays.
None of this makes the revenue data useless. “No revenue cliff across dozens of firms” is a genuinely reassuring finding. It just is not the same claim as “a four-day week raises revenue by X%,” and honest advisers should not let the second claim borrow the first claim’s credibility.
Self-selection is not a scandal, but it is a limit
Pilot firms opt in. They tend to be smaller, better prepared and led by people who already believe change is possible. That does not invalidate their results; it defines where the results apply. If your organisation is larger, more coverage-bound or starting from a more difficult place, expect your pilot to be harder and your percentages smaller. Plan for redesign support accordingly.
There is also a reporting effect. Organisations that struggled are quieter than organisations that succeeded. The UK’s 92% continuation at publication and the US/Ireland finding that no responding company planned to return are encouraging, but “responding” is doing work in that sentence.
How to build charts you can defend
Baseline everything for four to eight weeks before launch, ideally with a prior-year comparison for seasonal absence and revenue. Report absolute numbers and percentages together: “absence fell from 1.9 to 1.1 days per employee-month across 84 staff” survives scrutiny; “absence down 42%” alone does not.
Break results down by team, role and contract type. A firm-wide average can hide the one department whose workload never changed and whose stress rose. Set your decision rules in advance — for example, continue if customer response times hold, quality does not deteriorate, actual hours fall by at least 10%, and no subgroup is made worse off.
Finally, keep measuring after the announcement high fades. Novelty flatters early pulses. A three-month and six-month reading, honestly published including the flat lines, will do more for your credibility with staff and clients than any headline percentage borrowed from someone else’s pilot.
One further habit separates credible reporting from brochure copy: state the comparison period every time. Absence and resignations are seasonal, revenue more so, and a pilot that runs from spring to autumn is not being compared like-for-like with a winter quarter. The pilots handled this by choosing comparison periods explicitly. Your internal reporting should do the same, and should keep the raw monthly series visible behind any summary percentage so a sceptical finance director can see the shape of the change rather than a single flattering number.
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
Day5Group is a consultancy that assists in the transition to a 4 day work week. More about Day5Group · All blog articles