(CNBC) — There are just two weeks of summer left and if you haven't taken vacation yet you're not alone.
More than half of American workers left vacation days unused in 2015 according to a study conducted by Project Time Off, an organization started by the U.S. Travel Association.
Yet not taking a vacation could be adding to your stress—and hurting your career. The study found workers who took at least 11 days off a year were more likely to have received a raise or bonus in the past 3 years than those who took less than 10 vacation days.
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"Americans work really hard, but we need vacations to give us the break, so we can work smart," Katie Denis, senior director of Project Time Off told CNBC's "On the Money" in an interview.