The length of time that caffeine remains in the body will be different for everyone. Each person’s metabolism is unique, as is the speed at which their body processes and breaks down caffeine. Factors such as age, body weight, and individual sensitivity can also affect how long it stays in the system. In the average adult, it takes between 10-12 hours to completely eliminate caffeine from the system. Pregnant women are one exception to this—they metabolize it much more slowly. According to a study conducted in 2017, caffeine can stay in a pregnant woman’s body up to 16 hours longer than usual.