By Morten Hansen

There’s one big mistake people make all the time:

Working too many hours

As I report in Great at Work in a 2009 survey by Harvard Business School Professor Leslie Perlow and research associate Jessica Porter, 94% of the 1,000 professionals surveyed worked 50 hours or more a week, and a staggering 50 percent of them said they worked more than 65 hours a week. In a study of high earners, management writer Sylvia Ann Hewlett found that a full 35 percent worked more than 60 hours a week, and 10 percent worked more than 80 hours a week.

Working all of these very long hours only makes sense if it leads to better performance. But as I’ve experienced first-hand, it doesn’t. Early in my career, when I worked at the Boston Consulting Group, I put in 60, 70, 80, 90-hour weeks in an effort to make my mark. One day, I confronted an uncomfortable truth: A colleague of mine was getting better results than I was. Her analysis was crisper and more compelling. Yet one evening in the office, when I went to look for her, she wasn’t there. I asked a guy sitting near her desk where she was, and he replied that she’d gone home for the night. He explained that she never worked late. She worked from 8 a.m. to 6 p.m. No nights. No weekends.

This colleague was on to something. As my research has shown, performance doesn’t increase in a linear fashion with hours worked. Consider this chart.

I analyzed the relationship between weekly hours worked and performance among 5,000 managers and employees in my study. Working longer hours enhances performance, but only up to a point. If you work between 30 and 50 hours per week, adding more hours on the job lifts your performance. But once you’re working between 50 and 65 hours per week, the benefit of adding additional hours drops off. And if you’re working 65 hours or more, overall performance declines as you pile on the hours. (Note: these are averages across jobs and industries. The actual numbers may be different in your job, but consider that the shape is similar).

Other research has documented the same inverted “U.” Studying factory workers at a weaponry plant in Britain in 1914, Stanford economist John Pencavel found that performance topped out at 64 to 67 hours per week, beyond which it began to fall. Consider his chart shown below, and notice how similar it is to mine, even those these are very different data sets.

Think about the profound implication of these findings: the whole entire premise of the world’s work ethic—that harder work equates better results — is basically wrong. Yes, you need to work hard (about 50 hours per week in my dataset), but that’s completely different from saying you need to work harder than others to rise to the top.

What’s the implication for all of us? Are you working the right number of hours in the week? Too many, or too few? You should actually determine a number in your mind: “the optimal average number of hours per week to work for me is ___ .” Mine is 50. Then comes the most important question of all: how can I spend those hours of work better? As the top performers in our study showed, it’s how they work — and not how much they work — that counted the most to boost job performance.

Morten T. Hansen is a management professor at University of California, Berkeley. He is the author of Great At Work: How Top Performers Achieve Less, Work Better and Achieve More.

Originally published at

Sign up to receive daily news, inspiration, and advice on how to master work and life from Ladders