If you can't remember the last time you took a vacation, you're not alone.

More than half of U.S. workers who are offered paid vacation days won't use them all this year, according to a new report from Bankrate.com.

Workers are leaving a median of seven vacation days on the table.

The excuses for not taking company-provided time off varied: some workers blamed having too much work, others said they enjoyed their work, while others report they can't afford a vacation or fear they might lose their job.

Related: These companies offer paid vacation ... and pay for your vacation

But not using paid vacation days is like leaving money on the table and can backfire on someone trying to be a standout employee.

"If you don't take your time off, you can get burned out more easily and faster," said Sarah Berger, personal finance expert at Bankrate. "You can get sick and your relationships can suffer if you don't strike that work-life balance that will help you excel at work and in your career."

But for some workers, letting days to go unused is a strategic move -- 35% of those surveyed said they plan to roll over days to cover a big vacation or life event next year.

Related: These workplace benefits are slowly fading away

Younger workers are more likely to let vacation days go unused. Close to 60% of workers aged 18 to 25 report they won't use all of their allotted vacation days this year, while 25% won't use any of their time off.

Meanwhile, only 6% of Gen-Xers and 7% Baby Boomers report they wont use any vacation days.

"Many Millennials feel like they have something to prove and want to dispel these negative stereotypes that have labeled them as entitled or lazy," said Berger.

When it comes to cash versus paid time off, cash is king. The survey found that 56% of workers would rather have a cash bonus equal to one week of pay instead of time off.