Whether we work in cubicles, the C-suite, or a home office, we’re always navigating the people and cultural norms shaping our workday.

American workers are usually a pretty busy bunch, yet their time spent idle costs employers an estimated $100 billion per year, according to a new study from Harvard Business School.

“We suspected idle time might be more prevalent than most people would suspect,” says Teresa Amabile, Baker Foundation Professor at Harvard Business School. “But that $100 billion figure astounded us.”

Amabile co-wrote a paper on the topic, The Downside of Downtime: The Prevalence and Work Pacing Consequences of Idle Time at Work,forthcoming in the Journal of Applied Psychology with Andrew Brodsky, a former HBS doctoral student who is now an assistant professor at McCombs School of Business at the University of Texas at Austin.

Despite such pitfalls of idle time, however, the phenomenon has been understudied. “There is much more focus on the opposite—having too much to do in too little time,” says Amabile. “We wanted to investigate idle time, in part, to raise everyone’s awareness of how widespread and pernicious it can be.”

With the help of survey firm GfK, Brodsky and Amabile took a representative sample of people across 29 occupations—including lawyers, managers, agricultural workers, and soldiers. They found that 78 percent of employees reported experiencing some kind of idle time. Moreover, in every one of the 29 occupations, at least 50 percent of the GfK respondents experienced idle time.

Converting those hours into wages, the researchers conservatively estimated that such idle time costs businesses a whopping $100 billion a year.

Idle, not lazy

They make the distinction between idle time and leisure time or procrastination, which are voluntary in nature. “We are talking about time at work when employees are supposed to be working, and available to work, but they are unable to,” says Brodsky. “With idle time, the organization is often hurt by it, and it’s not enjoyable for employees either.”

Involuntary idle time can have a variety of causes, including built-in excess capacity, in which a company intentionally schedules more workers than it needs as insurance against busy times—for example, at a call center in which the number of calls fluctuates. In other cases, however, managers may allocate work poorly, leaving employees with nothing to do, or equipment could malfunction or break down, leaving workers unable to complete necessary tasks.

Such moments of forced idleness can be just as painful as stress from overwork, Brodsky says. “There is an optimal level of psychological arousal—we don’t want to be overstimulated, but we don’t want to be under-stimulated.”

Adds Amabile, “Some idle time can be welcome to someone who has been working hard. But we humans get bored pretty quickly.”

In order get a better handle on how employees react to being idle, Brodsky and Amabile conducted several experiments. “We had people do what we thought was one of the most boring tasks imaginable—copy sentences,” Brodsky says. To make it more unpleasant, they inserted typos that participants had to copy exactly. They then took away any possible distractions such as phones or the internet, so that any time they had after finishing the task would be idle.

Dragging of feet

Despite the tediousness of the task, the researchers found that when participants realized that they would have much more time than they needed, they intentionally slowed their work to fill it, preferring the tedious task to the prospect of doing nothing. Their performance, however, did not improve, no matter how much time they took. They simply drew out the time to avoid idleness.

What’s more, says Amabile, “they really dragged their feet as they got closer to the end of the task.”

Brodsky and Amabile dubbed that phenomenon the “deadtime effect,” in contrast to the oft-observed “deadline effect” that sees workers’ productivity increase in response to a time limit.

That deadtime effect is particularly problematic for the workplace since it implies that workers will slow down their work rather than risk appearing idle—making it difficult for managers to tell how much work employees actually have and leaving them no capacity for unexpected new tasks that could pop up.

The last experiment Amabile and Brodsky conducted, however, holds out some hope for overcoming the deadtime effect. In one condition in this study, participants were told that if they finished the task early, they could surf the internet.

“That expected leisure time changed things completely,” says Amabile. Participants worked much more productively, finishing the same tasks in less time but without any more mistakes—and without any evidence of the “deadtime effect.”

Less focus on hours, more on outcomes

The researchers conclude that strategic use of leisure time could help counteract the negative effects of idle time in the workplace as well. For that to happen, managers must encourage transparency, so they know how much work employees are actually doing, and not punish them for finishing work faster.

“Managers should evaluate employees based on outcomes rather than hours spent working or seeming to work,” Brodsky says.

When employees don’t have work to do, managers can reward them by allowing them to surf the internet, read, or play video games or ping pong. “Access to leisure activities, once work has been completed, need not detract from productivity if it’s done right,” Amabile says.

For managers concerned that offering such activities might lead to distraction or procrastination, they can be offered in public space separate from the working area. “Then it’s obvious when someone is in the leisure area, and it’s fun for them to hang out with others who have also completed their work,” Amabile says.

Encouraging such leisure time would not only make workers more productive by giving them something to look forward to, Brodsky and Amabile say, but it would also help managers as well. They would then have a more realistic view of how long tasks take and which employees have extra capacity, allowing them to allocate work better and recoup costs from unnecessarily idle time.

This article originally appeared on Harvard Business School Working Knowledge.