Child Growth Percentile Calculator (UK-WHO)
Calculate child height, weight, and BMI percentiles using UK-WHO growth charts. Identify if your child's growth is on track.
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Child Growth Guide
What's the key thing to understand about Understanding Percentiles?
Growth percentiles compare your child to a population of healthy children of same age and sex. 50th percentile: average. 50% of children weigh/measure less; 50% weigh/measure more. 25th-75th percentile: 'normal middle range.' Not too tall or too short relative to peers. 9th-91st percentile: typical range — 82% of healthy children fall within. Below 0.4th or above 99.6th: outside expected range — discuss with GP. UK-WHO growth charts: used by NHS Red Book. Based on healthy breastfed babies and children from multiple ethnic backgrounds, making them broadly representative of the UK population.
What Matters More Than Percentile?
Tracking trend more important than single measurement. A child at 25th percentile who has always been at 25th percentile is normal — they are constitutionally smaller but healthy. A child at 50th who drops to 25th over 6 months may have an underlying issue — investigate. Crossing two percentile lines: discuss with GP. May indicate: chronic illness, eating disorder, malabsorption, hormonal issue, family changes (stress). Mid-parental height: genetic prediction of adult height. Boys: (mother's height + father's height + 13cm) ÷ 2. Girls: (mother's height + father's height − 13cm) ÷ 2 — a rough genetic estimate, not a guarantee, since many other factors influence final adult height.
What's the key thing to understand about BMI in Children?
Adult BMI categories (over 25 = overweight, over 30 = obese) DO NOT apply to children. Children's BMI must be interpreted against age and sex percentiles. Healthy weight: BMI 2nd-91st percentile. Overweight: 91st-98th percentile. Obese: above 98th percentile. Underweight: below 2nd percentile. Note: child BMI percentiles use different cut-offs than adult absolute BMI values. A child with BMI 25 may be in the healthy range if they are tall for age. Childhood obesity in the UK: roughly 1 in 4 children entering primary school (age 4-5) are already overweight or obese, rising to over 1 in 3 by the time they leave primary school.
When to Be Concerned?
Speak to GP if: weight loss in a child (not normal — only happens in illness). Crossing two percentile lines either way over 6 months. Persistently below 0.4th or above 99.6th percentile. Big difference between height and weight percentile (e.g. 90th for height, 10th for weight). Refusing food. Eating disorders. Excessive thirst, urination (diabetes screening). Slowed growth before puberty (constitutional delay vs hormonal issue). Health visitor and GP have access to growth chart records. Use the Red Book — the NHS personal child health record — to track measurements over time, since a single measurement matters far less than the trend across several checks.