Great question. I run a productivity software startup, and my cofounder brought up the 4-day week idea. We opted not to pursue it. It came down to a few things:

- Onboarding / Collaboration overhead (this compounds) An additional dev is one more to manage, one more to onboard, one more to keep happy, buy hardware and software licenses for, and all that for the same number of man-hours.

- Work compounds. A programmer working on a system or feature for 10 days does the deepest learning in days 7-10. The internals, nitty-gritty stuff. For a 3 day a week employee, the same insights are gained in week 4 (10 days) instead of week 2 (10 days). Of course, I used 10 days as an example, but true expertise is built and compounded over months. It doesn’t matter how many 3-day-a-week hires we have, this process won’t be sped up.

- Compensation / Performance - how do we do this in an equitable way? Again, comes down to compounding impact. If 5 day a week employee makes 5/8 of the impact at the same productivity rate as 3 day a week employee - does that mean they get promoted / rewarded at a different rate?

- Availability / Scheduling - 30 hours is about 3.5 work days a week. It’s an added pain to manage and track who is going to be working when. If your company uses a system for taxes, payroll, vacation accrual, insurance, etc, chances are it is built for 8 by 5 employees first and foremost.

- Various laws around part time and full time workers, based on hours in some jurisdictions. I think 28 hours is the cutoff here in Ontario?