The recommended BMI for a teenage boy cannot be given without a specific age, as the BMI for a teenage boy is based on his age, notes the CDC. A healthy BMI is anywhere from the fifth to 85th percentile, but there is no exact number for every teenage boy.
BMI scores are not a diagnostic tool; they are simply a tool used to screen for health problems such as obesity, according to the CDC. For example, a 15-year-old teenage boy with a BMI of 15 falls in the underweight category, while a 10-year-old boy with a BMI of 15 is in the normal range. A teenager who scores high in BMI is not necessarily considered overweight or unhealthy. A doctor must do an exam to account for things such as physical activity level and diet. A BMI calculator specifically for children and teens may be found on the CDC website.