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Children's Health

Child & Teen
BMI Calculator

Unlike adults, children's healthy weight range changes with age and sex. This calculator uses NHS centile charts to give you an age-adjusted result and explains what it means for your child's growth.

Calculate now → Speak to a GP
Ages 2–18 supported
NHS centile method
Growth Chart · BMI-for-Age Live
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Alex, 9 yrs
Male · 135cm · 30kg
16.5
BMI
BMI Percentile Chart · Age 2–18
Healthy Weight
52nd
Percentile
9 yrs
Age
15–19
Healthy range
📏 Child & Teen BMI Calculator

For children and young people aged 2–17. Results are based on NHS UK90 centile charts and adjusted for age and sex.

ℹ️ Child BMI is interpreted differently to adult BMI. A result is compared against other children of the same age and sex — the centile position matters more than the BMI number itself.

For children aged 2–17 only. For adults (18+) please use our Adult BMI Calculator. This tool is a guide only — always discuss results with your GP.

How child BMI works
UnderweightBelow 2nd centile
Healthy weight2nd – 91st centile
Overweight91st – 98th centile
Very overweight (obese)98th centile or above

The centile shows how your child's BMI compares to other children of the same age and sex in the UK. A 50th centile means half of children have a higher BMI and half a lower one — it says nothing about height or muscularity.

Under
Healthy
Over
Obese
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BMI (kg/m²)
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Centile
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Age
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Height
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Weight
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Speak to your GP
Your GP can provide a full assessment in context of your child's growth trajectory, diet, activity level, and overall health.
This result is a guide only and uses an approximate centile estimation. NHS centile charts involve sex-specific lookup tables — precise centiles require clinical assessment. This tool does not replace medical advice. Please speak to your GP.
Supporting healthy growth

What matters most for children's health

Weight is just one part of the picture. These factors support healthy growth and long-term wellbeing.

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Physical Activity
Children aged 5–17 should aim for at least 60 minutes of moderate-to-vigorous activity daily. This supports healthy weight, bone development, and mental wellbeing.
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Balanced Diet
Plenty of fruits, vegetables, wholegrains, and lean protein — alongside limiting sugary drinks and ultra-processed foods — supports healthy growth without restrictive dieting.
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Screen Time
Excessive sedentary screen time is linked to increased snacking and reduced sleep quality. Balancing screen use with active play is encouraged by NHS guidelines.
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Sleep
Children aged 6–12 need 9–12 hours of sleep per night; teens 8–10 hours. Poor sleep disrupts appetite-regulating hormones and can contribute to weight gain.
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Body Image & Wellbeing
How you discuss weight with children matters enormously. Focus on health, energy, and strength — not size or appearance — to support positive body image.
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GP Assessment
If you're concerned about your child's weight or growth, your GP can review their growth trajectory over time — a single measurement is rarely the full picture.
Non-Emergency Medical Advice
NHS 111
For urgent medical questions that aren't life-threatening — available 24 hours a day, 7 days a week online or by phone.
Life-Threatening Emergency
999
Call 999 immediately if a child is experiencing a medical emergency such as difficulty breathing, loss of consciousness, or severe allergic reaction.