People who make a lot of money feel stressed about the amount of time they have to spend it, according to the economist Daniel Hamermesh.

Rich people have more incentive to work a lot, since they are sacrificing more dollars per hour by not working than lower earners.

Even when they don't work, higher earners feel pressure to spend their time on costly experiences.

Lower earners feel less stressed about how they spend their time, but more stressed about actually making money.

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Stress at work has an income divide.

Higher earners work more because they feel rushed to make and spend money, while lower earners feel less stress over work, according to the economist Daniel Hamermesh, who recently released his book "Spending Time: The Most Valuable Resource."

On average, Americans have more money than they had 50 years ago, Hamermesh argued, but they have the same 24 hours in a day to spend it. Median household incomes have increased in the past 50 years (though real wages haven't budged). The time we spend on things like sleeping, eating, and personal grooming hasn't changed substantially.

"Our incentives drives us to do things differently," Hamermesh said in an interview with Business Insider. "The amount of income we have, which differs substantially across people, leads us to spend the time differently as we have differently."

Read more: While CEOs like Jack Ma and Elon Musk praise grueling job schedules, employees around the world are demanding shorter workweeks

On top of the already scarce amount of time Americans have, the US works harder than other developed nations. European countries like France and Germany have mandated paid vacation days. Even Japan, where people have died from working too much, created a national holiday and encouraged companies to allow their employees to leave early on Fridays.

The US, meanwhile, is the only advanced economy that does not have a federal paid-vacation policy.

High-income earners have more options for spending their money compared with low-income earners — so when you have a lot of money, you can be stressed about how you're going to spend it.

When they eventually do take time off, higher earners have so much money saved that they have an incentive to spend it on things that cost a lot of money per hour. Rich people today are investing their money less in designer goods and more in luxury lifestyles, such as high-end gym memberships, multimillion-dollar vacations, and exclusive hotels.

Read more: 15 top companies that let you have a life outside of work

Therefore, higher earners get stressed because they feel as if they don't have enough time for the costly leisure activities they think they need.

"We really can't cut back on things too much," Hamermesh said. "While our incomes [keep] on going up, we feel more and more rushed."

On the flip side, low-income earners feel less rushed, as they don't have the money to spend on luxury travel or experiences. In his book, Hamermesh said he found that lower earners spent more time watching TV and sleeping than higher earners.

While lower earners aren't stressed about the time they have to spend either working or relaxing, they are stressed about their income. A UBS study found that more and more people in the bottom 60% of income earners have reported feeling "stressed," and the American Psychological Association found in 2014 that the stress gap between the rich and poor had widened in the past few years.

"I'm not sympathetic with the rich guy who says how stressed he is. He could choose to work less, give away his income, and he wouldn't be as rushed for time," Hamermesh said. "On the other hand, the low-income individual just isn't living very well. To me, that's much more important."