Every four-day week announcement creates two audiences. Full-time staff hear “same pay, one day less.” Part-time staff do a quick calculation: if my colleague now works 32 hours for the salary she got for 40, her hour is worth 25% more. What happens to mine?
If the answer is “nothing,” you have built a two-tier workforce on day one. Headline support can look strong — 97% of staff in the US and Ireland 2022 pilots wanted to continue — while a fairness problem builds quietly and surfaces as grievance and part-time attrition.
The arithmetic nobody puts in the slide deck
A full-timer on $52,000 moves from 40 hours to 32 at the same salary. Her effective rate rises from $25.00 to $31.25 an hour. A part-time colleague working 24 hours at $25.00 earns $600 a week. Leave her rate unchanged and she does similar work alongside someone at $31.25 an hour. That gap is arithmetic, not perception.
Three responses are common; only two work.
Do nothing. Cheapest this quarter, costliest within a year: predictable hour-increase requests, hard part-time recruitment and a permanent “them and us” story.
Pro-rata hourly uplift. Raise part-time hourly rates by the same proportion (here, 25%, to $31.25; $750 a week for 24 hours). Hours stay as contracted; the hour is valued equally. Organisations that have published their pilot designs, including non-profits that reviewed them openly, often choose this.
Offer restructuring choice. Let part-timers pick the uplift, a pro-rata hours cut at the same weekly pay (24 hours to roughly 19), or a move toward full-time on the new pattern where vacancies allow. Choice costs more to administer, but part-time hours exist for different reasons — caring, study, health, phased retirement — and one answer rarely fits all.
Half-measures fail transparently. A 10% uplift against a 25% full-time gain will be found within a week. Publish the principle: an hour of work is worth the same here, whatever the contract.
Quieter equity traps
Leave. Counted in “days” while schedules vary, leave accrues and spends unevenly. Convert all leave to hours at pilot start and publish the rule for public holidays falling on non-working days.
Opportunity access. Training, acting-up duties and visible projects land on days someone is off. Audit who receives them across the pilot, or the shorter week will slow part-timers’ progression — a penalty many already face.
Premiums and bonuses. Weekend premiums on a 40-hour base and bonus thresholds assuming five days of contact need rebasing, checked rather than assumed.
New joiners. A vacancy advertised as “four-day week” that is really pro-rata part-time at the old rate will be discovered at offer stage, and the story will travel.
Iceland’s trials (more than 2,500 public workers, 2015–2019) cut hours from 40 to 35–36 with pay held, then extended shorter hours through collective agreements covering most of the workforce. The lesson is not the number; it is that the change lasted as a workforce-wide norm, not a gift to one contract group. Perpetual Guardian in New Zealand made its 2018 trial permanent after monitored results showed stress falling from 45% to 38% and work-life balance scores rising from 54% to 78% — again as an organisational standard, not a subset perk.
Actionable steps
- Cost the uplift before announcing the model — part-time uplift, leave-in-hours conversion and premium rebasing in the pilot budget. Boards trust honest numbers over late corrections.
- Write the equal-hour principle into the trial terms and trace every rule back to it.
- Offer structured choice where possible — uplift, hours reduction, or uplift-only status quo — and document each election for payroll and rotas.
- Convert leave to hours on day one, with the public-holiday rule for every pattern.
- Track equity cuts during the pilot: absence, overtime, internal moves, training access and leavers split by part-time and full-time, never just a blended average.
- Ask part-time staff at the decision point whether the design feels fair. Hesitation means you do not have consent for permanence, however good the aggregates look.
A four-day week is sold as fairness with time. If the people already working the shortest weeks gain nothing, the story fails. Price the equity fix into the business case from the start — it is far cheaper than rebuilding trust afterwards.
Sources
- UK 2022 pilot — Autonomy / Cambridge / Boston College, 21 February 2023: https://www.sciencedaily.com/releases/2023/02/230221113132.htm
- US and Ireland pilots 2022 — 4 Day Week Global, December 2022: https://www.internationalworkplace.com/community-zone/news/four-day-week-pioneering-pilot-program-a-huge-success-new-research-reveals
- Iceland trials 2015–2019 — Autonomy / Alda, July 2021: https://phys.org/news/2021-07-shorter-week-boost-productivity-burnout.html
- Perpetual Guardian, New Zealand, 2018: https://www.sciencealert.com/this-4-day-work-week-experiment-went-so-well-company-keeping-it-perpetual-guardian-engagement-balance
Day5Group is a consultancy that assists in the transition to a 4 day work week. More about Day5Group · All blog articles