Child BMI Percentile & Obesity Class Calculator (AAP 2023)

About this tool

This calculator works out body mass index (BMI), BMI percentile and obesity class for children and teens aged 2 to 19 years. It is meant for clinicians who want a quick, guideline-based classification and a summary of the recommended evaluation and treatment.

You choose sex and age, then enter weight and height. BMI is compared with CDC 2000 BMI-for-age data. Under the 5th percentile is underweight, the 85th to under the 95th percentile is overweight, and the 95th percentile or above is class 1 obesity. Class 2 starts at 120% of the 95th percentile or a BMI of 35, and class 3 at 140% of the 95th percentile or a BMI of 40. Because z-scores are unreliable above the 97th percentile, the tool also reports BMI as a percent of the 95th percentile.

For overweight and obesity, the result lists evaluation steps such as blood pressure at every visit and, from 10 years with obesity, lipids, glucose or HbA1c and ALT. Treatment follows the AAP 2023 clinical practice guideline (Hampl et al., Pediatrics 2023): intensive health behavior and lifestyle treatment, medicines offered from 12 years, and surgery evaluation from 13 years in selected teens. Titration schedules for semaglutide, liraglutide, phentermine-topiramate and orlistat are shown.

Common questions

How are class 2 and class 3 obesity defined in children?

Using AAP 2023 classes, class 1 is a BMI at or above the 95th percentile. Class 2 starts at 120% of the 95th percentile or a BMI of 35, and class 3 at 140% of the 95th percentile or a BMI of 40. Classes 2 and 3 are called severe obesity.

At what age can obesity medicine be offered to children?

Per the AAP 2023 guideline as summarized in the tool, pharmacotherapy should be offered from 12 years of age to children with obesity, alongside lifestyle treatment. Medicines listed include semaglutide, liraglutide, phentermine-topiramate and orlistat.

When should a teen be evaluated for bariatric surgery?

The tool suggests metabolic and bariatric surgery evaluation from 13 years of age for teens with class 3 obesity, or class 2 obesity with a significant comorbidity, based on the AAP 2023 guideline.

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