Knowing how many calories are in a meal when you eat out may help you decide what to order. And with more restaurants now required to post the calories, it’s getting easier to find out just what you’re getting, right? Maybe not. Those calorie counts can be off. Way off!

Researchers from Tufts University analyzed 29 dishes from 10 restaurant chains, including Ruby Tuesday, McDonald’s, and Wendy’s. They found, on average, the meals had 18 percent more calories than what was listed on the menu. The differences ranged from 36 percent fewer calories to a whopping 200 percent more!

So… it’s probably best to use those calorie counts just as a rough guideline. Don’t count on them entirely.