Teen BMI Percentile Calculator

BMI for teenagers (ages 2–19) is calculated using the same formula as adult BMI, but the interpretation is fundamentally different. Instead of fixed cutoffs, teen BMI is evaluated using age- and sex-specific percentiles from CDC growth charts, because body composition naturally changes with age and differs between boys and girls during puberty.

BMI formula (same as adults): BMI = Weight (kg) ÷ Height (m)²

Or in imperial units: BMI = (Weight (lbs) ÷ Height (inches)²) × 703

Teen BMI interpretation, percentile-based:

• Below the 5th percentile: Underweight
• 5th up to 85th percentile: Healthy weight
• 85th up to 95th percentile: Overweight
• 95th percentile and above: Obese

Read those boundaries carefully, because they are inclusive at the bottom. Landing exactly on the 5th percentile is healthy, not underweight, and landing exactly on the 95th is obese, not overweight. It is an easy thing for a calculator to get backwards.

Where:

• Percentile compares the child’s BMI to other children of the same age and sex in the CDC reference population
• Age must be used as a third variable, unlike adult BMI which only uses weight and height
• Sex matters because boys and girls have different BMI-for-age charts, reflecting different body composition through puberty

Why adult BMI cutoffs don’t apply to teens: A 14-year-old boy with a BMI of 22 sits comfortably in the healthy range, a little below the 85th percentile for his age. Hand that same BMI of 22 to a 10-year-old boy and it lands near the 90th percentile, which is overweight. Nothing about the body changed; only the reference group did.

Worked example: 14-year-old girl. Weight: 130 lbs (59.0 kg). Height: 5'3" (63 inches = 1.60 m).

• BMI = (130 × 703) ÷ 63² = 91,390 ÷ 3,969 = 23.0
• On the BMI-for-age reference for 14-year-old girls, that lands at roughly the 83rd percentile
• Interpretation: Healthy weight, between the 5th and 85th percentiles, though close enough to 85 to be worth rechecking in six months

That last point is the useful part. A percentile in the low 80s is not a problem, but it is a different situation from one in the 40s, because BMI-for-age tends to track: a teenager near a boundary at 14 is often past it at 16. The number to watch is the direction of travel across two or three measurements, not any single reading.