It’s not just the sugar in chocolate that gives you an energy boost. Chocolate has about 20 to 30 milligrams of caffeine per ounce, which adds up to about 100 milligrams in a bar—the same as a cup of joe. It only takes 15 minutes for the jolt to hit your bloodstream, but it takes six hours for your body to eliminate just half a dose of caffeine. So prepare to be energized—and be wary of too much chocolate before bedtime.

MORE: The Real Scoop on Caffeine in Candy