Teen BMI Percentile Calculator

BMI for teenagers 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. The same is true from age 2; this page covers 13 to 19.

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: Obesity
• 120% of the 95th percentile and above: Severe obesity (class 2), and 140% and above is class 3

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 obesity, not overweight. It is an easy thing for a calculator to get backwards.

Above the 95th the CDC’s 2022 extended charts stop quoting a percentile and measure BMI as a percentage of the 95th instead, because the old curves bunch together up there. The American Academy of Pediatrics 2023 guideline uses the same classes, and so does this page.

How the percentile is worked out: the CDC publishes three numbers for each month of age, L (the skew), M (the median BMI) and S (the spread). The z-score is ((BMI ÷ M)^L − 1) ÷ (L × S), and the percentile follows from it. This page uses the CDC’s own values every six months from 12 to 20 years, with a straight line in between, so it gives the same answer as the Child Growth Percentile Calculator, which adds height and weight percentiles from age 2.

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, at about the 81st percentile for his age. Hand that same BMI of 22 to a 10-year-old boy and it lands at about the 95th, the edge of the obesity range. 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.