The majority of Americans are making this huge mistake that can hold them back at work

Saving your vacation time can do more harm than good. Unfortunately, the majority of working Americans haven't gotten the memo, yet.

According to a new Project: Time Off study conducted by consumer research company GfK Public Affairs, the average US worker took 16.2 days of paid time off last year, which is down from the more than 20 days workers took off between 1976 and 2000. What's more, 55% of the over 5,600 working Americans surveyed left vacation days unused in 2015.

This is the first time the US Travel Association's initiative found a majority of American workers are not using all their vacation time. Last year's survey showed 42% of Americans were leaving vacation time on the table.

According to the report, Americans didn't take 658 million vacation days and lost 222 million of them entirely because they couldn't be rolled over, paid out, or banked for any other benefit.

Project: Time Off estimates that, by giving up this time off, Americans forfeited $61.4 billion in benefits. It also suggests that these unused vacation days could have generated $223 billion in spending for the US economy.

What's more, numerous previous studies suggest that not taking enough vacation time is bad for your health, happiness, productivity, and prospects for a promotion. Another recent study found that not taking enough time off is especially damaging to our interpersonal relationships.

Part of the problem is that people see their earned vacation time as a luxury and not a right. According to the new Project: Time Off study, 80% of employees said if they felt fully supported and encouraged by their boss, they would be likely to take more time off. Conversely, 65% of employees report that they hear nothing, mixed messages, or discouraging messages about taking time off.

"The culture of silence has created a vacuum, and American workers have filled that vacuum with the pressure they put on themselves," study author and senior director of Project: Time Off, Katie Denis, writes.

"The single-most important step workers can take is to plan their time off in advance," she concludes.

People who set aside time to plan how they'll use their vacation time each year tend to use more of their time than those who don't: 51% of planners took all of their vacation time, compared to 39% of non-planners who took all their vacation time. Planners are also more likely to take a full week of vacation time or more at a time.