There are many open questions in science -- Are we alone in the universe? What's at the bottom of a black hole? When will I finally get my jetpack? -- but according to Rest, a new book by Stanford's Alex Pang, 'How many hours a day should a knowledge worker work?' isn't among them.

Decades of science and a whole host of historical luminaries have all come to the same conclusion: if your work involves your brain, then the right answer is just four hours.

Don't believe me? Then maybe this short Guardian article from consistently fascinating journalist Oliver Burkeman will convince you. In it, he boils down the impressively persuasive case for not trying to wring more than four hours of creative work out of your brain each day. It consists, essentially of three types of evidence.


First, formal research backs up Pang's assertion. Have you heard of the 10,000 rule? You'd think the need for so much practice would run counter to the idea that four hours of intellectual work a day maxes out our brains. But according to Burkeman, when the same guys who conducted the research on which Malcolm Gladwell based his famous dictum studied the schedules of violinists, they found a hard limit on each practice session.

Elite performers might rack up an impressive amount of practice, but science shows they do it in chunks of four hours or less.


Science might have documented this four-hour maximum fairly recently, but apparently geniuses in a wide range of fields have intuited it for centuries.

"Charles Darwin worked for two 90-minute periods in the morning, then an hour later on; the mathematician Henri Poincaré from 10am till noon then 5pm till 7pm; the same approximate stretch features in the daily routines of Thomas Jefferson, Alice Munro, John le Carré and many more," writes Burkeman.

Hunter gatherers

It seems even our pre-industrial forbearers may have been wiser than us when it comes to understanding the brain's natural rhythms. Even though hunting gazelles seems a long way from hammering out investment deals, they too were subject to the brain's four-hour work limit -- only they were smart enough not to try to fight it.

"Half a century ago, the anthropologist Marshall Sahlins caused a stir by suggesting that people in hunter-gatherer societies aren't ceaselessly struggling for survival," reports Burkeman. "Crunching numbers from Africa and Australia, he calculated the average number of hours hunter-gatherers must work per day, to keep everyone fed. That's right: it was 'three to five hours'."

What to do with the other four hours

The case for your brain having a built in maximum for concentration and creativity is pretty compelling, but that doesn't necessarily mean you could or should lounge around for the rest of the day. When our brains are tapped out, we can still profitably spend time refilling them with new knowledge, catching up with our inboxes, pursuing hobbies, or powering through mindless but essential administrative work.

But if you're constantly trying to power through substantive knowledge work for eight hours or more a day, then it's pretty much guaranteed that you're wasting a whole lot of time.