What does the BMI Calculator for Children do?

Calculate BMI for children aged 2-18 with age and gender-adjusted interpretation. All calculations are performed in your browser using official UK rates and thresholds.

Is this medical advice?

No. This calculator is for informational purposes only and does not constitute medical advice. Always consult your GP or an appropriate healthcare professional for medical guidance.

Are the reference values from the NHS?

Where applicable, this calculator uses reference values and guidelines from the NHS and other UK health authorities. Individual needs may vary based on personal health circumstances.

BMI Calculator for Children

Calculate BMI for children aged 2-18 with age and gender-adjusted interpretation.

Last updated: April 2026 · Source: NHS — BMI calculator for children

Age (2-18)

Gender

Height (cm)

Weight (kg)

BMI for age 8 boy

15.9

Healthy weight

Children's BMI is interpreted differently from adults — it's compared against growth charts for age and sex. This is an approximation. For accurate results, use the NHS child BMI centile tool or ask your GP/health visitor.

Disclaimer

This calculator is provided for informational purposes only and should not be considered as financial or tax advice. All calculations are performed locally in your browser — no personal data is collected or sent to our servers. Rates and thresholds are sourced from HMRC and GOV.UK and are updated for the current tax year. Always verify results with HMRC or consult a qualified professional before making financial decisions.

How It Works

BMI-for-age in children is calculated using the same formula as adults (weight in kg ÷ height in m²), but the result is then plotted against age-and-sex-specific growth charts to give a centile. Unlike adult BMI, a fixed number does not define overweight or obese — what is healthy changes as children grow.

The NHS uses the UK-WHO growth charts for children aged 2–18. A BMI above the 91st centile is classified as overweight, and above the 98th centile as obese. Below the 2nd centile may indicate underweight. The calculator returns the centile and classification based on these thresholds.

Children's body composition changes significantly during puberty, so centile tracking over time is more informative than a single reading. If you are concerned about your child's weight, the NHS recommends speaking to your GP or health visitor, who can plot measurements on official growth charts and advise on next steps.

Example: Girl aged 10, 35 kg, 140 cm

BMI: 35 ÷ (1.40)² = 35 ÷ 1.96 = 17.9
Plot on UK-WHO girls' chart at age 10
Centile: approximately 65th centile
Classification: Healthy weight (between 2nd and 91st)

Source: NHS — BMI calculator for children

Frequently Asked Questions

What does the BMI Calculator for Children do?: Calculate BMI for children aged 2-18 with age and gender-adjusted interpretation. All calculations are performed in your browser using official UK rates and thresholds.
Is this medical advice?: No. This calculator is for informational purposes only and does not constitute medical advice. Always consult your GP or an appropriate healthcare professional for medical guidance.
Are the reference values from the NHS?: Where applicable, this calculator uses reference values and guidelines from the NHS and other UK health authorities. Individual needs may vary based on personal health circumstances.