From never-ending deadlines to impromptu projects, employees are working harder than ever—and their vacations are suffering. Recent surveys from Kelton Research for Radisson and travel websites like Expedia and Hotwire report that U.S. workers on average won’t use two of their vacation days (sometimes up to a week’s worth) by the end of the year.

That equals 226 million unused days in total, or $34.3 billion worth of time, according to estimates from CNNMoney.

Why aren’t employees using their vac days for, say, relaxation on white sandy beaches? Some say taking a vacation is too expensive, while others claim heavier workloads are forcing them to forgo time off.

Carol Evans, President of Working Mother Media, asserts that employees should always take all of their vacation days. “Your vacation time is part of your pay package,” she says. “Not taking all of your days is like giving part of your paycheck back to your company.”

Another job-related price to pay for skipping your vacation: Not allowing yourself to re-energize can result in decreased work performance down the road. “Your vacation time is an opportunity for you to renew, refresh, think, plan and dream,” adds Evans. “You need that uninterrupted time to spend with your family to form important memories. That in itself is priceless.”

So the next time you’re contemplating working extra hours instead of taking some much-needed vacation time, rethink it. “Your vacation time has been negotiated and earned by you, just like your paycheck,” Says Evans. “Honor its value.”

We want to know: Do you skip your vacation days because of a heavy workload? Let us know in the Comments section.