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Fill in the details on the left and click Calculate BMI to see your child's result.
How Child BMI Is Calculated — and Why It's Different
BMI (Body Mass Index) is calculated using the formula: BMI = weight (kg) ÷ height² (m²). For adults, this single number is compared against fixed thresholds (18.5, 25, 30). For children, however, a single threshold is meaningless — a 5-year-old and a 15-year-old have very different healthy body compositions.
This is why paediatricians use BMI-for-age percentile charts. These charts, developed by the CDC using data from thousands of children, show how a child's BMI compares to peers of the same age and sex. A child at the 85th percentile weighs more than 85% of children their age — but whether that's healthy requires clinical context.
The four categories — Underweight (<5th percentile), Healthy Weight (5th–85th percentile), Overweight (85th–95th percentile), and Obese (≥95th percentile) — are the standard thresholds recommended by the American Academy of Pediatrics, WHO, and India's paediatric guidelines.
This calculator supports children aged 2 to 19 and accepts both metric (cm, kg) and imperial (ft/in, lb) inputs. It also calculates the healthy weight range for your child's height, giving you a practical target rather than just an abstract number.