BMI Calculator for Teens
BMI for children and teenagers, read against age and sex percentiles rather than adult thresholds — because the adult categories do not apply.
The BMI formula is the same, but the interpretation is completely different.
How the bmi calculator for teens works
The BMI formula is the same, but the interpretation is completely different. A growing child's healthy BMI changes year by year, so the figure is compared against a percentile chart for their age and sex rather than a fixed number.
This uses the standard percentile bands: under the 5th is underweight, 5th to 85th healthy, 85th to 95th overweight, above the 95th obese. The percentile estimate here is approximate — a clinician reading the actual growth chart is the definitive assessment.
Formula: BMI = kg/m², read against an age-and-sex percentile chart
Worked examples
| Inputs | BMI | Note |
|---|---|---|
| A 14-year-old, 163 cm, 54 kg | 20.32 | BMI 20.3 — healthy for that age |
| A younger child | 15.87 | the healthy BMI is much lower at 8 |
| An older teenager | 22.72 | approaching adult thresholds |
FAQFrequently asked questions
Why is BMI different for children?
Because body composition changes throughout growth. A healthy BMI at 6 is very different from one at 16, so a fixed threshold cannot work.
What is a BMI percentile?
Where a child sits compared with others of the same age and sex. The 50th percentile is the median.
What percentiles are healthy?
The 5th to the 85th. Below the 5th is underweight; the 85th to 95th overweight; above the 95th obese.
Is this a diagnosis?
No. It approximates the growth chart. A clinician reading the actual chart, with the child's growth history, is the proper assessment.
When do adult thresholds start applying?
At 20. Between about 18 and 20 the percentile bands and adult thresholds converge.
Where these figures come from
- Mifflin MD et al., "A new predictive equation for resting energy expenditure in healthy individuals", Am J Clin Nutr 1990 — the BMR equation used here
- World Health Organization — Waist circumference and waist–hip ratio (2008 expert consultation) — waist-to-hip cut-offs
- Tanaka H, Monahan KD, Seals DR, "Age-predicted maximal heart rate revisited", J Am Coll Cardiol 2001 — 208 − 0.7 × age
- Nathan DM et al., "Translating the A1C assay into estimated average glucose values" (ADAG), Diabetes Care 2008 — eAG = 28.7 × A1c − 46.7
- Mosteller RD, "Simplified calculation of body-surface area", N Engl J Med 1987 — BSA = √(height × weight / 3600)
- Australian Department of Health and Aged Care — national health guidance
Last checked: September 2026. The equations are fixed by their published papers and do not change with tax years or regulations; the thresholds quoted in verdicts name the body that set them.