Industry
The four-day week and the math of leave
Blasko Sarcevic
Founder, Time-Out Zone ·
The four-day week is usually discussed as a culture question: productivity, recovery, recruiting. The part almost nobody talks about is the bookkeeping underneath. The moment a team moves to four days, the value of every single vacation day changes, and most leave balances quietly keep calculating wrong.
Topic
Four days instead of five: why the leave balance must re-count.
A vacation day is not a fixed unit
On a five-day week, 20 vacation days equal four weeks off. If the same person moves to four working days per week and keeps the 20 days, they suddenly have five weeks off: each day became more valuable, because a week now only costs four days.
The fair conversion is proportional: 20 days on a five-day schedule equal 16 days on a four-day schedule. Both give four weeks off. Skip the conversion and you silently shift entitlement between full-week and four-day staff, and you notice only when someone does the math.
Where the balances break
Most leave balances are built around one assumption: everyone works the same five days. A four-day week violates that assumption in three places. First, deduction logic: a Friday off must not cost a vacation day for someone who never works Fridays. Second, public holidays: when a holiday lands on the fixed day off, the compensation question appears. Third, carry-over: balances earned on the five-day schedule need converting at the switch date.
In spreadsheets this gets messy fast, especially when a team runs mixed models: some on five days, some on four, some on 4.5. At that point every person needs their own work schedule as the basis of the leave calculation, not a company-wide assumption.
Hours instead of days?
Some companies solve the problem by tracking leave in hours: 160 hours instead of 20 days. That is precise but hard to communicate, because people plan vacations in days and weeks. The workable middle ground: calculate internally per person in the working days of their own schedule, and use the week as the display unit. Four weeks off is the number that stays comparable across every model.
A checklist before the switch
Teams introducing a four-day week should settle the leave math before the effective date, not after.
- Convert entitlements proportionally and publish the formula (20 on 5 days = 16 on 4 days).
- Convert existing balances at the switch date instead of carrying them over unchanged.
- Deduct only for scheduled working days: the fixed day off never costs vacation.
- Decide the holiday rule: what happens when a public holiday lands on the day off?
- Store per-person work schedules in the system so the math is automatic.
Editorial piece. The conversion logic is standard proportional math; statutory minimums per country are unaffected. Not legal advice.
Related
Leave balances that understand schedules
Time-Out Zone calculates per person, from their work schedule: four-day weeks, part-time, and mixed models without spreadsheet special cases.