If you’re putting in a 60-hour workweek, you may think the people who do their regular 40 hours and go home are slackers — but the truth is, they’re probably more productive than you are.

Back in the early 1900s, Ford Motor Co. ran all kinds of tests to find out how many hours a week would produce the best results from employees. Forty hours was found to be the so-called “sweet spot,” and while adding another 20 hours did produce a minor boost in productivity, it was temporary — in fact, after about a month, those people were actually less productive.

Upper-management executives in the US point to the long workweeks in countries like Thailand, Korea and Pakistan as examples of “working more means more work gets done,” but studies show that in six of the top 10 most competitive countries in the world — Sweden, Finland, Germany, the Netherlands, Denmark and the UK — there are actually laws on the books prohibiting employees from working more than 48 hours a week.

In other words, don’t feel guilty if you put in your eight hours and go home. You’re actually doing your part to keep productivity high.

[Time]