BMI Calculator for Kids

Enter your child's gender, age, height, and weight to calculate their BMI for Kids. This tool uses CDC growth chart data to return your child's BMI value, BMI percentile, and weight category (Underweight, Healthy Weight, Overweight, or Obese) for children aged 2 to 9 years.

Disclaimer: This tool is for informational and educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before making any health-related decisions.

Gender *

years

Enter your child's age in whole years

months

Optional: enter extra months beyond full years

ft
in
lbs

Results

BMI Value

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BMI Percentile

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Weight Category

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Healthy BMI Range for Age & Gender

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Results Table

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Frequently Asked Questions

What is BMI and why is it calculated differently for children?

BMI (Body Mass Index) is a measure of weight relative to height. For children, BMI is interpreted using age- and sex-specific percentiles (called BMI-for-age) because children's body fat changes as they grow, and boys and girls differ in body fat levels as they mature. A single BMI cutoff like adults use doesn't apply to kids.

What do the BMI percentile categories mean for my child?

According to CDC guidelines: below the 5th percentile is Underweight, 5th to below 85th is Healthy Weight, 85th to below 95th is Overweight, and 95th percentile or above is Obese. These categories help gauge a child's weight status relative to other children of the same age and gender.

Can I use this calculator for children under 2 years old?

No. This calculator is designed for children aged 2 to 9 years. For infants and toddlers under 2, weight-for-length charts from the WHO are used instead of BMI-for-age. Consult your pediatrician for assessments of children under 2.

What should I do if my child's BMI is outside the healthy range?

If your child falls in the Underweight, Overweight, or Obese categories, you should consult your child's pediatrician or a registered dietitian. BMI is a screening tool, not a diagnosis. A healthcare provider will consider your child's full medical history, diet, physical activity, and growth trends before making any recommendations.

Does BMI accurately measure body fat in children?

BMI is a useful screening tool but does not directly measure body fat. It does not distinguish between muscle mass and fat, nor does it account for ethnic background or physical activity level. A child with a high BMI may have more muscle, while a child at a normal BMI may still have excess body fat. Always combine BMI results with a professional health assessment.

Why does gender matter when calculating BMI for kids?

Boys and girls develop at different rates and have different proportions of body fat at the same age. The CDC uses separate growth chart percentile curves for males and females to account for these differences, which is why gender is a required input for an accurate BMI-for-age percentile.

How is BMI calculated for children?

The formula is the same as for adults: BMI = (weight in lbs × 703) ÷ (height in inches²). However, the result is then compared to a CDC reference population of children of the same age and sex to produce a percentile, which determines the weight category. It's this percentile — not the raw BMI number — that matters most for kids.

How often should I check my child's BMI?

Most pediatricians check BMI at every annual well-child visit. You can use this calculator between visits to track trends, but a single reading is less meaningful than watching how percentile tracks over time. Sudden jumps or drops in percentile are worth discussing with your child's doctor.