Knowing you need a vacation is one thing. Finding the time to take it is another.

And finding the time to plan it--ugh. That’s even worse. So it’s understandable that, after a long morning locked in meetings, you might think it’s time to start planning your mountain biking trip.

Don’t do it. New research suggests those flights of fancy are likely to cost you more than you intended--and that you’ll enjoy your vacation less than if you had booked it while not at work.

Ajay Kalra, a professor of marketing at Rice University’s Jones School of Business, and Wei Zhang, an assistant professor at Iowa State’s College of Business, used data from a major online hotel booking site to figure out what happens when you book travel from work. The researchers examined 4,582 reservations, of which 35 percent were made during work hours. The travelers all paid for the bookings at the time they made their reservations. In order to exclude most of the business travel, the researchers only included trips that included a major holiday or a weekend.

Those who made reservations during business hours chose higher-quality, more expensive hotels. Maybe psychologically they felt they deserved a treat. The researchers also cite the increasingly popular study of decision fatigue, which shows that our resistance to temptation declines after we’ve had to make a lot of decisions--no matter how trivial those choices may seem at the time.

"We speculate that occurs because people are either more fatigued at work and tend to buy more expensive items, or that vacations seem more appealing while people are at work," Kalra says. "This kind of preliminary data indicates that people should not be making purchases when they are working."

But here’s the kicker: Those who booked their stays during work hours were, in the end, less pleased with their vacations than those who booked after-hours. So not only did they spend more money, they had a less enjoyable time.

What if there’s no cut-off between your work and nonwork hours? In that case, there’s only one clear choice: Ask someone else to book your vacation. Be super-nice to them, even if you're not 100 percent thrilled with every single one of their choices. You're getting to go away, after all. And, hey, bon voyage!