For the study, researchers analyzed 3,300 teens’ and adults’ sleep schedules over five years and calculated that for every extra hour that teens stayed awake, they would gain about 2.1 points on their body mass index (BMI). BMI is a scale that’s used to measure a person’s body fat based on their height, weight, and gender, and ranges from underweight (less than 18.5) to morbidly obese (30 or greater). The researchers also found that teens were still susceptible to weight gain if they stayed up late and slept in later the next day. These findings held regardless of the time the teens spent exercising, or on their computers, cell phones, tablets, or other electronic devices. If they stayed up late, they were more likely to gain weight.