How do you calculate BMI for a teenager?+
Teen BMI uses the same formula as adult BMI: weight in kilograms divided by height in metres squared. The key difference is interpretation. Instead of comparing the result to fixed adult thresholds (18.5, 25, 30), you compare it to the CDC BMI-for-age percentile chart for your teen's age and sex. A BMI of 23 could be healthy for one teen and overweight for another depending on their age and sex.
What is a normal BMI for a 14-year-old?+
For a 14-year-old male, healthy BMI is between 16.6 (5th percentile) and 23.4 (85th percentile). For a 14-year-old female, healthy BMI is between 16.4 and 23.4. These CDC cutoffs apply regardless of height. The actual healthy weight range in kilograms or pounds depends on the teen's specific height, which this calculator computes automatically based on the percentile cutoffs.
What BMI is overweight for a 15-year-old girl?+
A 15-year-old female with a BMI at or above 24.0 falls at the 85th percentile and is classified as overweight by CDC guidelines. A BMI at or above 27.7 places her at or above the 95th percentile (obese category). These thresholds are age and sex specific. They differ from the adult overweight threshold of 25, which should not be applied to teenagers.
Is BMI accurate for teenage athletes?+
BMI is less accurate for athletic teens because it cannot differentiate muscle from fat. A teen who participates in strength sports, swimming, or competitive athletics may have a BMI in the overweight range due to higher muscle mass, without excess body fat. Pediatricians who work with teen athletes often supplement BMI with skinfold measurements or waist circumference to better assess body composition. Use BMI as a starting point, not a final judgment.
What is underweight for a teenager?+
A teen is classified as underweight when their BMI falls below the 5th percentile for their age and sex. For a 15-year-old male this is below 17.2, and for a 15-year-old female below 17.0. Underweight teens may not be getting enough calories or nutrients to support healthy growth and development. Persistent underweight, especially with symptoms like fatigue, hair loss, or menstrual irregularities in girls, warrants medical evaluation.
How does puberty affect BMI percentile?+
Puberty causes rapid, uneven growth. Weight often increases before the corresponding height growth spurt, temporarily pushing BMI higher. Then height catches up and BMI drops back. This is completely normal. A teen who appears overweight at age 13 may return to a healthy percentile by age 15 as their height increases. This is one reason the CDC recommends evaluating BMI trends over time rather than relying on a single reading taken during a growth phase.
Should I worry if my teen's BMI is at the 85th percentile?+
The 85th to 95th percentile is classified as overweight and warrants attention, but it is not an emergency. Start by discussing it with your teen's pediatrician at the next well-visit. The doctor will assess whether the BMI reflects actual excess body fat or is related to muscle mass, growth stage, or measurement timing. If dietary habits or activity levels are areas for improvement, small gradual changes tend to be more sustainable and less psychologically harmful than strict interventions.
What does CDC BMI-for-age percentile mean?+
A percentile indicates where a measurement falls relative to a reference population. A BMI at the 60th percentile means the teen has a higher BMI than 60% of teens the same age and sex in the CDC reference sample, and a lower BMI than the remaining 40%. The CDC 2000 Growth Charts used by this calculator are derived from representative US survey data (NHANES) collected between 1963 and 1994, before obesity rates rose significantly, making them a stable clinical reference point.
Can I use the adult BMI calculator for my 17-year-old?+
No, it is not appropriate to use adult BMI thresholds for a 17-year-old. Adult BMI classification (overweight at 25, obese at 30) is calibrated for fully developed adult bodies and does not account for the growth and body composition changes that continue through adolescence. A 17-year-old male with a BMI of 25 is at approximately the 80th percentile, which is still within the healthy range for his age. Using adult thresholds would incorrectly classify him as overweight.
What is the CDC BMI percentile data source?+
This calculator uses the CDC 2000 Growth Charts, which are the official reference charts published by the US Centers for Disease Control and Prevention (CDC) and recommended by the American Academy of Pediatrics (AAP). The charts are based on NHANES (National Health and Nutrition Examination Survey) data and represent the BMI distribution of US children and adolescents. They are the standard reference for pediatric BMI screening in the United States.
My teen is 18 or 19 - should I use this calculator or the adult BMI calculator?+
The CDC growth charts extend to age 19, so this calculator is appropriate for 18 and 19-year-olds. At age 20, the adult BMI thresholds (18.5 for underweight, 25 for overweight, 30 for obese) are typically applied. The transition from age-specific to adult thresholds around age 19-20 means that the adult and teen thresholds align reasonably closely by late adolescence, with the 85th percentile for 18-19 year olds being very close to the adult overweight threshold of 25.