Child & Teen BMI Percentile Calculator

Why children use percentiles, not adult BMI categories

BMI is calculated the same way at every age — weight in kilograms divided by height in metres squared. What changes is how it is read. Because children and teens are still growing, CDC expresses their BMI relative to others of the same sex and age; these values are called BMI-for-age percentiles (CDC). Healthy BMI changes a lot through childhood, so the same number can mean very different things at 4 and at 14.

A percentile shows where a child sits within CDC's reference population. If a child's BMI is at the 75th percentile, 75% of children of the same sex and age in that population had a lower BMI (CDC). Race is not a factor in calculating BMI percentiles. CDC's adult categories, which use fixed BMI cut-offs, apply only from age 20 (CDC).

What each category means

CDC places children and teens in these categories, using its own wording (CDC):

For severe obesity, CDC also shows the American Academy of Pediatrics' expanded definition: Class 2 Obesity is 120% to less than 140% of the 95th percentile, or BMI 35 kg/m² to less than 40 kg/m²; Class 3 Obesity is 140% of the 95th percentile or greater, or BMI 40 kg/m² or greater (CDC).

The original 2000 growth charts stop at the 97th percentile. For children with very high BMIs, CDC developed extended percentiles in 2022, based on data for children and adolescents with obesity from 1988 to 2016 (CDC). This calculator uses that extended method above the 95th percentile, which is why it also shows BMI as a percentage of the 95th percentile.

How to measure height and weight accurately at home

Accurate measurements are essential for a correct BMI and BMI percentile. CDC recommends (CDC):

Height

• Remove shoes, bulky clothing, hats and hair ornaments, and undo hairstyles that get in the way.
• Stand the child on firm flooring (tile or wood, not carpet) against a flat wall with no molding.
• Feet flat and together against the wall, legs straight, arms at the sides, shoulders level, looking straight ahead.
• Lower a flat, rigid ruler or book at a right angle to the wall until it touches the top of the head, with your eyes level with it. Lightly mark the wall and measure from the floor with a metal tape measure.
• Record the height to the nearest ⅛ inch or 0.1 centimeter.

Weight

• Use a digital scale rather than a spring-loaded bathroom scale, on firm flooring rather than carpet.
• Remove shoes and heavy clothing, such as sweaters.
• Have the child stand with both feet in the center of the scale, and record the weight to a decimal (for example, 55.5 pounds or 25.1 kilograms).

Limitations of BMI in children

• BMI percentile is not intended to be a sole diagnostic measure. It is one part of the overall picture, alongside other screening results, genetics and behaviors such as diet, physical activity and sleep (CDC).
• BMI cannot distinguish between fat, muscle and bone mass, all of which affect weight (CDC).
• The reference population is historical: the 2000 BMI-for-age charts are based on data from 1963–1980 for most children (CDC).
• Different calculators can round age, height and weight differently, so results may differ slightly between programs (CDC).

When to talk to a doctor

Talk to your child's health care provider about their BMI; it may relate to overall health and well-being (CDC). The American Academy of Pediatrics and Bright Futures recommend that pediatric providers check BMI for all children 2 years and older at least once a year, which is a good chance to talk about growth (CDC).

A BMI calculator is not a substitute for professional medical advice (CDC). If your child's result is outside the Healthy Weight category, or you have any questions about their growth, ask their doctor.

How this calculator works

Age is counted in completed months between the date of birth and the date of measurement, the way CDC's Child and Teen BMI Calculator does, and must be 24 to 239 months (2 through 19 years). Each month uses CDC's reference values for that month (CDC).

Up to the 95th percentile, the percentile and z-score come from CDC's LMS parameters for the 2000 growth charts. Above it, they come from CDC's 2022 extended method, which uses a separate dispersion value for each sex and month (CDC). As in CDC's calculator, the category is chosen from the percentile rounded to the nearest whole number, so a percentile of 84.6 is reported as the 85th (Overweight). Reference data downloaded from cdc.gov on 1 October 2026.

Frequently asked questions