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Australian Kids BMI Calculator

Calculate your child's BMI and age-adjusted percentile using the same growth chart reference used in Australian paediatric practice.

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Screening tool only. BMI percentile is a screening tool, not a diagnosis. A result outside the healthy range does not mean your child has a health problem — speak with your GP or paediatrician for any concerns. Not recommended for children under 2 years.
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UnderweightHealthyOverweightObese
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BMI Categories for Children

CategoryBMI percentileInterpretation
UnderweightBelow 5th percentileMay need assessment for nutritional needs or growth concerns
Healthy weight5th to <85th percentileBMI is within the healthy range for age and sex
Overweight85th to <95th percentileHigher than typical — discuss with your GP
Obese95th percentile or aboveSignificantly above typical — GP assessment recommended

Categories follow the CDC 2000 reference standards used in Australian paediatric growth chart assessments. BMI percentile is age- and sex-specific for children — unlike adult BMI which uses fixed cutoffs.

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For children and teenagers, BMI is interpreted differently than for adults. Because body fat changes with age and differs between boys and girls, Australian paediatric practice uses BMI-for-age percentile charts — the same CDC 2000 reference standards used in Australian growth chart assessments. A percentile tells you how your child's BMI compares to other children of the same age and sex: a 75th percentile means their BMI is higher than 75% of children their age. The healthy range is the 5th to 85th percentile. BMI is a screening tool only — a number outside the healthy range is a starting point for a GP conversation, not a diagnosis. Last updated May 2026.

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Frequently Asked Questions

Adult BMI uses fixed cutoffs (18.5, 25, 30) that apply regardless of age. In children, the amount of body fat naturally changes as they grow, and boys and girls develop differently. For this reason, children's BMI is compared against growth charts to give an age- and sex-specific percentile. A BMI of 17 might be in the healthy range for a 6-year-old but below healthy for a 15-year-old.
No — calorie-restrictive diets are not recommended for growing children without medical supervision. An overweight BMI percentile is a starting point for a conversation with your GP, not a directive to restrict food. In many cases, children in the overweight range simply grow into their weight as they get taller. Your GP may recommend focus on healthy eating, active play, and reducing sedentary screen time rather than dieting.
Yes. BMI measures weight-for-height and doesn't distinguish between fat and muscle. A child who is very active and muscular may have a higher BMI percentile without excess body fat. Similarly, a child can be in the healthy BMI range but still have a high proportion of body fat if they are very sedentary. BMI is a population-level screening tool — your GP will look at the full picture including growth trends, diet, activity, and family history.
For infants and toddlers under 2, growth is assessed using weight-for-length percentiles rather than BMI. The WHO Growth Standards provide separate charts for this age group. Your child's health nurse or GP will use these charts at routine checks (the Blue Book in most Australian states) to track your child's growth against expected ranges.
This calculator uses the CDC 2000 BMI-for-age reference standards (the same data used in Australian growth chart assessments) with linear interpolation between annual percentile values. Percentile estimates are accurate to within approximately 2–3 percentile points for most ages. For precise clinical assessment, your GP will use validated software or printed growth charts with your child's measurement history.