Edit: I simplified my math. I know there are 24 hours of work in a day. It's not about that. The point is about rhythm. 7 days is 100% If you'd work 7 days, t

Edit: I simplified my math. I know there are 24 hours of work in a day. It's not about that. The point is about rhythm. 7 days is 100% If you'd work 7 days, there's no downtime to recover. You simply just tear into your reserves, and get less productive each week until you hit diminishing "returns" in being less productive, getting to some low productive apathy state. It's productivity rock bottom. There are people who can manage this but very few can. 6 days 86%. Now you can rest for a day. Great! But there's still little time for socializing and other stuff in life. There's no way of flourishing at all. Also, if there's trouble but not enough trouble (e.g. bad sleep), then you'll be using that day and there's no socialization at all that week. Or time to spend on your hobbies. 5 days is 71%. Now you can devote 29% of every week on free time. Literally 29% of your life is free. You can now absorb fairly big shocks that aren't covered in illness protection plans. You also have time to get into a hobby. So why 4? The cyclical nature of the week makes it to be 57%. 43% is left to free time. I'm working this amount. If I include my vacation days with it, I work an exact 50% and am free 50%. I have sleep issues that no doctor cares to know about. My free day is on a Wednesday. If my sleep is screwed over then I can rest all day during a Wednesday or a Saturday. Sunday is always left over for free time. If I have a good week of sleep, then it can happen that I feel a bit bored. I have too much free time. It results in an iron clad focus on work. I've worked 5 days per week. I never had an iron clad focus as I was always struggling with sleep. If my sleep was screwed over on Monday, then I'd need to suffer until Friday. Now I only need to suffer until Wednesday and sometimes I even swap days and don't have to suffer at all. So that's a simple example of how it improves my focus. It's an example of how I'm probably more productive on 4 days than 5. Why more? Productivity drops by 50% for programmers with severe sleep deprivation. Different sectors and situations may have different results. But I'd suggest to try and sketch out different scenarios where it does and doesn't work. So why not 3? Well maybe 3. I can tell you why not 2, because it's extreme enough for me to see why. The context of work starts to fade. Your subconscious starts to deal with issues less to not at all (in the context of programming). It takes way longer to warm up. Why is this the case with 2? Because 2 days of work is only 29% of your week. Your identity will be formed around what you'll do in your free time. Work will become a "side thing". You will be amazingly well rested to work, provided you can manage your life well. But the extra increase in focus won't make up for it. The switch between 5 to 4 days may in certain cases may not up for it either, but in my particular case it's clear that it does.