BMI for Kids
WHO BMI-for-age z-score for kids 5β19. Color-coded category, parent guidance. Works offline.
About this tool
A BMI tool for kids and teens ages 5 to 19, built on the WHO Growth Reference 2007. Enter age in years and months, sex, height, and weight β the tool computes BMI, the WHO z-score (how far from the median a child of that age and sex sits), the percentile, and a color-coded category: underweight, healthy weight, overweight, or obese. Categories follow the WHO thresholds: thin below z = -2, healthy between -2 and +1, overweight between +1 and +2, obese above +2. A short parent-friendly guidance block is included for each category, with practical, non-restrictive advice (focus on habits, avoid dieting kids, involve the pediatrician). All math runs in the browser; the inputs are saved on your device for next time. Works fully offline.
Details
- Category
- Health & Fitness
- Version
- 1.0.0
- Size
- 25 KB
- Updated
- Jun 2026
Frequently Asked Questions
Why does a child need a different BMI tool?
Adult BMI uses the same thresholds for everyone (overweight at 25, obese at 30). Kids' bodies change as they grow, so the WHO uses BMI-for-age z-scores β how far a child is from the median BMI of other children the same age and sex. A 10-year-old and a 15-year-old with the same BMI can be in very different categories.
What are the cutoffs?
WHO categories for 5β19 years: thin (z-score below -2), healthy weight (-2 to +1), overweight (+1 to +2), obese (above +2). These are international standards, not country-specific.
How accurate is the z-score?
The tool uses the official WHO LMS parameters (L, M, S) for BMI-for-age by sex, sampled yearly from 5 to 19 years with linear interpolation between. For exact percentile readings, ask your pediatrician β they can plot BMI on a full WHO chart.
Should I act on the result?
BMI is one signal among many. It does not measure body composition (muscle vs fat), puberty timing, or ethnicity differences. Use it as a starting point for a conversation with your pediatrician rather than a verdict.
Is my child's data private?
Yes. Age, sex, height, and weight are saved only in this browser via localStorage. Nothing is uploaded, so the tool works fully offline.