Americans tend to overestimate how many hours they work in a typical week by about 5 to 10 percent, according to study published in a Labor Department journal, with the biggest exaggerators being people who work longer weeks.

The study compared people’s estimates for how much time they spent working against a time diary they were asked to keep of all their activities. Whether because of faulty memories or a desire to sound more industrious (or some combination of the two), most respondents systematically overestimated how much time they spent at work.

The typical person who reported having worked 40 hours, for example, actually worked closer to 37. The report found that “The greater the estimate, the greater the overestimate”; people who said they worked 75 hours actually worked closer to 50 hours. (That’s an overestimate of 25 hours, or 50 percent!) At the other end of the spectrum, people who worked relatively few hours (under around 25) actually ended to underestimate their hours.

Here’s a chart taken from the report showing the number of hours that survey respondents said they worked on the horizontal axis, and the amount by which they over- or understated their actual hours:

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The study notes that overestimates of working hours have been found in other countries as well, including Belgium, Russia, China and Japan.

Americans are also bad at properly estimating their time spent on other activities, including housework. A 1998–2001 national diary study found that people grossly exaggerated how much time they spent on housework. Men estimated spending a total of 23 hours on housework per week, versus the 10 hours they actually spent when forced to keep a time diary. Women estimated 32 hours versus 17 hours in the diary.

The margin of exaggeration for work hours has changed over time. It spiked in 1985, when the average person overstated his or her time spent working by 6.2 hours.

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(Hat tip: Harvard Business Review)