I often see statistics that "people are only productive four hours/day", but they never seem to cite their sources. The studies I've tracked down are low quality (example). 30 minutes poking around google scholar produced nothing useful.

Where are the high quality studies showing how long people can work productivity?

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Adam Zerner



Note: I'm going to be talking about productivity in the sense of hard work. Eg. Anders Ericsson's idea of deliberate practice.

It seems self-evident that if you're performing busywork like data entry or cleaning, you could be productive for way longer than four hours/day.

It also seems self-evident that in doing something in between busywork and hard work, you can still be productive for more than four hours/day. For example, a calculus student doing tons of practice problems, or an experienced web developer building a simple sign up form.

So then, it seems to make sense to me to deal with the question of hard work. Pushing yourself to the edge of your comfort zone, or perhaps slightly beyond it. For example, mastering a difficult new concept or skill.

Of course, when we talk about hard vs easy work, we're talking about a spectrum, so "hard work" really refers to a general area in that spectrum, not a single point. The answer to the question of how many productive hours you have in a day probably depends a little bit on where exactly you are on that spectrum, but getting into that nuance seems like something more appropriate for a different question. Here, it seems like it's worth just grouping "hard work" together and treating it as a single thing.


Note: As jimrandomh mentions, things like age, physical health and motivation probably matter, as do things like performance enhancing substances or techniques. It seems to me like it'd make sense to address those things in different question though. Eg. here I think we can ask the question of how many productive hours a healthy individual who isn't doing any performance enhancing stuff has in a day. Then in a separate question, we can ask how things like age and physical health impact this number. And in another separate question, we can ask how things like performance enhancing substances impact the number.


After about an hour of googling around, I haven't been able to find any of those high quality studies either. My impression is that the "people are only productive for four hours/day" idea largely comes from interviewing successful people, as opposed to rigorously measuring their performance. If there were high quality studies that really measured performance, I'd expect that they would be talked about more and easier to find, so I take the fact that they're hard to find as reasonably strong evidence that they don't really exist.

It is interesting to note that across a wide range of experts, including athletes, novelists, and musicians, very few appear to be able to engage in more than four or five hours of high concentration and deliberate practice at a time.

This quote comes from a Harvard Business Review article titled The Making of an Expert. The authors are K. Anders Ericsson, Michael J. Prietula, and Edward T. Cokely. I know that Ericsson is known as an authority in the study of expert performance; not sure about the other authors.

The article Why you should work 4 hours a day, according to science also had some relevant excerpts. The author mentions various examples of experts reporting that four hours/day is their limit, and that in interviewing people, this is the strong pattern.


After his morning walk and breakfast, Charles Darwin was in his study by 8 a.m. and worked a steady hour and a half. At 9:30 he would read the morning mail and write letters. At 10:30, Darwin returned to more serious work, sometimes moving to his aviary or greenhouse to conduct experiments. By noon, he would declare, "I've done a good day's work," and set out on a long walk. When he returned after an hour or more, Darwin had lunch and answered more letters. At 3 p.m. he would retire for a nap; an hour later he would arise, take another walk, then return to his study until 5:30, when he would join his wife and family for dinner.


Toulouse noted that Poincaré kept very regular hours. He did his hardest thinking between 10 a.m. and noon, and again between 5 and 7 in the afternoon. The 19th century's most towering mathematical genius worked just enough to get his mind around a problem — about four hours a day.

G.H. Hardy:

G.H. Hardy, one of Britain's leading mathematicians in the first half of the 20th century, would start his day with a leisurely breakfast and close reading of the cricket scores, then from 9 to 1 would be immersed in mathematics. After lunch he would be out again, walking and playing tennis. "Four hours' creative work a day is about the limit for a mathematician," he told his friend and fellow Oxford professor C.P. Snow.

John Edensor Littlewood:

Hardy's longtime collaborator John Edensor Littlewood believed that the "close concentration" required to do serious work meant that a mathematician could work "four hours a day or at most five, with breaks about every hour (for walks perhaps)."

Ericsson's study of violin students:

Add these several practices up, and what do you get? About four hours a day. About the same amount of time Darwin spent every day doing his hardest work and Hardy and Littlewood spent doing math.
This upper limit, Ericsson concluded, is defined "not by available time, but by available [mental and physical] resources for effortful practice."

The article also makes some more general statements about the four hours/day idea:

Darwin is not the only famous scientist who combined a lifelong dedication to science with apparently short working hours. We can see similar patterns in many others' careers

In particular, it mentions the following study:

A survey of scientists' working lives conducted in the early 1950s yielded results in a similar range. Illinois Institute of Technology psychology professors Raymond Van Zelst and Willard Kerr surveyed their colleagues about their work habits and schedules, then graphed the number of hours spent in the office against the number of articles they produced. You might expect that the result would be a straight line showing that the more hours scientists worked, the more articles they published. But it wasn't.
The data revealed an M-shaped curve. The curve rose steeply at first and peaked at between 10 to 20 hours per week. The curve then turned downward. Scientists who spent 25 hours in the workplace were no more productive than those who spent five. Scientists working 35 hours a week were half as productive as their 20-hours-a-week colleagues.

If you search through Cal Newport's blog, you'll find lots of other examples of expert performers only being able to manage four hours/day of hard work. John Grisham’s 15-Hour Workweek is one:

Grisham primarily writes his novels during the winter months on his farm in Oxford, Mississippi. During this period he works five days a week, starting at 7 am and typically ending by 10 am.

There is something important that I'd like to emphasize. From what I can tell, all of these examples of expert performers who can only perform about four hours of hard work per day, these people all seem to be getting the other parts of the productivity equation right. They're sleeping enough, taking naps, taking walks, eliminating distractions, quitting Facebook, etc. So four hours/day seems like it is conditional on those things. I think that this is worth noting because many of us are not getting those things right. I know I'm not.



Why I believe this

1. The book "daily rituals", and references therein. People at the apex of achievement seem to work - at maximum intensity, not drone tier busy work - not much more than 4 hours a day. You would think that if it were possible to do more someone would, and they would surpass them.

The typical day would be 4 hours of damn hard creative work, 4 hours of taking care of business, 4 hours of fun. A good life.

2. I go looking for exceptions that do work really hard (deliberate practice hard) and they are few and far between. They seem either to burn out (Proust - died in his early 50s) or use serious drugs (Erdos - amphetamines) or seriously affect their health (Richard Stallman).

3. That study that I can't find right now that the violinists that made it practiced for about 4-5 hours a day. They were able to eke out an extra hour by napping in the middle.

4. My own experience. OK I am not that young anymore but 4 hours a day knocks me out. I am very happy to achieve 4 hours a day. I have been tracking this and average about 2.5/day, gradually going up

When people hear about the 4 hours thing they tend to think it is far too low. My advice to people is to try to get to 4 hours and *then* worry about going past it. If you can actually work maximally hard for 4 hours a day you will kill it. If you try to go past the 4 hours your brain will find ways to "procrastinate".

Also note that IMHO you cannot "carry forward" the 4 hours. Use it or lose it. At least that is my experience. Maybe you can do 3,5,4, etc but not much more, not 2,6,0,8.

I am interested in any other exceptions apart from the ones I listed above.

I would emphasise that you can be productive for far more than 4 hours a day. For example doing routine clerical work. But there does seem to limits on work at deliberate practice level or above. If you disagree, install Anki on your phone and download or make a deck of some things you are interested in memorizing. Keep adding cards until you have done 4 hours according to Anki (clock time may be 50% longer as you goofed off at various times without realizing it). Now do this for a week and report back.

Often people will say they practice violin for 6 hours, but you will usually find that there is a lot of down time in there.



The place I got this statistic (or something like it) from was the RescueTime blog. Here is the easiest-to-find post I could find in 60 seconds making the claim, and other blogposts might poke at it more.

The most relevant quote:

One of the biggest mistakes so many of us make when planning out our days is to assume we have 8+ hours to do productive work. This couldn’t be further from the truth.
What we found is that, on average, we only spend 5 hours a day working on a digital device.
And with an average productivity pulse of 53% for the year, that means we only have 12.5 hours a week to do productive work.

I'm hoping for something that can definitively say "productivity drops after N hours", or at least examines that question, rather than "we checked and people only do N hours of work/day". Maybe people can do more than N if they feel like it, in which case it's not a matter of how much the brain is capable of but of motivation.

Nod. I recall seeing studies making more concrete claims about burnout, overtime, etc, which seem more like what you were claiming. I can't do more than google randomly for such studies at the moment which seemed less useful. I also don't recall those studies matching the claims about 4 hours in particular. (That said, another source of the four-hour thing is the book Peak, which claims you get four hours of deliberate practice a day, which is a somewhat different claim)

But note that RescueTime's data only covers time spent on a computer, which is only a subset of productive work time; there are also meetings, work on paper, and things like that.



It heavily depends on how hard one's work is and how much time one has. From my personal experience:

1. I used to learn English around 5-8 hours everyday by reading native books that I did not understand.

2. I studied Japanese during three days for 10 hours each day, which resulted in 300 kanji learned in total.

Taking that into account, my personal opinion is that four hours/day is not a border, and one needs to explore his limits on his own.

2 Related Questions

4Answer by Elizabeth
If all of the following conditions are met: * It's mid-afternoon * I've previously been able to focus on the project. * I can't focus and just seem to keep checking social media. I either need a nap or to leave for a room with less carbon dioxide.
" But I don't have anything better to use for my actual goal, which is a measurable task that taxes creativity and *nothing else* " Maybe I'm reading this wrong, but why would one want to tax creativity? Seems to me that for the most part, creativity will have a lot of public good characteristics -- though I suppose one might suggest creative destruction is a better view...
Tax as in "a heavy demand", not "a charge usually of money imposed by authority on persons or property for public purposes". https://www.merriam-webster.com/dictionary/tax
7Answer by gwern
A good anthology to read is Creativity, ed Vernon 1970 - it's old but it shows you what people were thinking back when Torrance was trying to come up with creativity tests, and the many psychometric criticisms back then which I'm not sure have been convincingly resolved.
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This question seems like the tip of an iceberg of complexity. The workers' age, physical health and motivation probably matter. The contents of their non-work lives probably matter. In the case of programming, slightly degraded performance might mean enough bugs to be net negative, or it might just mean doing the same thing slightly slower. Caffeine-use patterns probably matter; use of other stimulants probably matters, too. In my own life, I've seen my personal productivity range from 80 hours/week to 0 hours/week over multi-month spans.

Agreed. I'd love to see data on all of those as well.

Update: found a relevant book, have ordered from library.

Update to the update: the book is focused on manual labor, which faces different limits than thought work.

I am actually curious on whether there is any evidence on the degree to which the two differ.

My personal experience is that physical and intellectual labor come out of almost entirely different pools. I'm curious if anyone experiences differently.

I do think it's possible that willpower to push yourself in either comes from a shared pool, but since I also think willpower is borrowing future productivity, optimum productivity over long periods of time uses very little.

Cool! I'd love to hear what you find!

It seems worth clarifying what you mean by "productive". As Raemon and waveman mention, the answer will depend on whether you are talking about "hard" work a la Anders Ericsson's idea of deliberate practice, or about more routine type of work. I suspect that you are talking about the former and that people will interpret it as the former, but it still seems worth clarifying.

It also might be worth mentioning that you are referring to "standard" cases of healthy individuals who aren't using any performance enhancing drugs or anything like that. I took that as a given, as the question of how unnatural things like that could change the default seems like a different question, as does the question of how things like anxiety or lack of sleep reduce your capacity.

These kinds of questions feel premature, given the absolute lack of data. I'd be interested in "returns drop off after N hours of deliberate practice" or "meetings go net negative after M minutes."