Enter your child's date of birth, measurement date, height, weight, and sex to get their BMI, BMI percentile, and weight category plotted against CDC growth standards. You'll see whether your child falls in the Underweight, Healthy Weight, Overweight, or Obesity range for their age and sex — plus a breakdown of their z-score and percentile rank.
BMI
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BMI Percentile
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BMI Z-Score
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Age Used
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Weight Category
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BMI percentile compares your child's BMI to other children of the same age and sex in a reference population. For example, a child at the 75th percentile has a BMI higher than 75% of children the same age and sex. Unlike adults, children's healthy BMI ranges change with age, which is why percentiles are used instead of fixed cutoffs.
According to CDC guidelines: Underweight is below the 5th percentile, Healthy Weight is the 5th up to the 85th percentile, Overweight is the 85th up to the 95th percentile, Obesity is at or above the 95th percentile, and Severe Obesity is a BMI at or above 120% of the 95th percentile value for age and sex.
BMI is a useful screening tool but does not directly measure body fat. Very athletic children may have a high BMI due to muscle mass rather than excess fat. BMI should be considered alongside a child's medical history, growth trend, diet, physical activity, and a healthcare provider's clinical assessment — not as a standalone diagnosis.
If the calculator shows your child is overweight or obese, the best next step is to speak with your child's pediatrician. They can assess the full picture — including growth trends, family history, and lifestyle factors — and recommend appropriate dietary changes, physical activity goals, or further evaluation if needed.
This calculator is designed for children and teens between 2 and 19 years of age, consistent with CDC growth chart standards. For children under 2, different WHO length-for-age and weight-for-age charts are used, and for adults 20 and older, a standard adult BMI calculator is more appropriate.
A Z-score (also called a standard deviation score) measures how many standard deviations a child's BMI is from the median BMI for children of the same age and sex. A Z-score of 0 means exactly at the median, while +2 is approximately the 97th percentile. Z-scores are often used in clinical and research settings because they can describe values beyond the 97th or below the 3rd percentile more precisely than percentiles alone.
Small differences can occur due to rounding in age, height, or weight, and the specific reference data or interpolation method used. This calculator uses CDC 2000 LMS reference values. Your healthcare provider's software may use slightly different rounding rules or chart versions. Always treat any online result as a screening estimate rather than a clinical diagnosis.
Focus on building healthy habits for the whole family rather than placing emphasis on a number. Encourage daily physical activity, offer balanced meals with fruits, vegetables, whole grains, and lean proteins, limit screen time and sugary drinks, and ensure adequate sleep. Positive, non-shaming conversations about health work better than diet-focused approaches for children.