In children, BMI is interpreted as a percentile because body fat changes with age and differs between boys and girls. Below the 5th percentile is underweight, 85th–95th overweight and the 95th or above obesity.
How to use the BMI Percentile Calculator for Children and Teens
- Sex
- Age
- Weight
- Height
Results update as you type, and every field accepts the units shown in its menu.
How it works
Enter sex, age, weight and height.
Tips
- Measure lying length for babies under 2 and standing height from age 2.
- Use the exact age in months for babies – a few weeks matters.
- Follow the trend across several visits; crossing two major percentile lines is more important than one value.
- Discuss concerns with your paediatrician.
Common mistakes to avoid
- Comparing a baby with the wrong sex chart.
- Reading the 50th percentile as “normal” and everything else as abnormal.
- Using corrected age incorrectly for premature babies.
Inputs explained
| Field | What to enter |
|---|---|
| Sex | Choose one: Male, Female |
| Age | Units: years, months |
| Weight | Units: kg, lb, st, g |
| Height | Units: cm, in, m, ft, mm |
What each result means
- BMI = [Weight]÷([Height]÷100)^2
- BMI percentile = ncdf([BMI-for-age z-score])×100
Example values
How the main result changes when Age changes and everything else stays at the example values above:
| Age (years) | BMI percentile (%) |
|---|---|
| 4 | 88 |
| 6 | 86 |
| 8 | 75 |
| 10 | 58 |
| 12 | 37 |
| 16 | 5 |
Health note: this calculator is for education and screening only and is not a diagnosis or treatment advice. Discuss your results with a qualified clinician.
Formula
BMI = weight ÷ height²
z = ((BMI ÷ M)^L − 1) ÷ (L × S), with CDC LMS values for age and sex
Percentile = Φ(z) × 100
Worked example
Inputs — Sex: Male; Age: 8 years; Weight: 28 kg; Height: 128 cm.
Results — BMI = 17.1; BMI-for-age z-score = 0.69; BMI percentile = 75 %; Weight status = Healthy weight; BMI as % of the 95th percentile = 85 %.
Key terms
- Percentile
- Share of children of the same age and sex with a lower value.
Frequently asked questions
What BMI percentile is healthy for a child?
Between the 5th and 85th percentile.
What is severe obesity in children?
A BMI at or above 120% of the 95th percentile.
Which charts are used?
The CDC 2000 BMI-for-age growth charts for ages 2–20.