Children and teens
Child BMI calculator: BMI-for-age percentile (ages 2 to 19)
Enter a child or teen’s age, sex, height and weight to get their BMI, their BMI-for-age percentile on the CDC growth charts, and the weight category it falls in.
Enter your values above to see your result and what it means.
Why children’s BMI is a percentile
Body fat changes as children grow, and it develops differently in boys and girls, so the same BMI can be healthy at one age and high at another. Instead of fixed cut-offs, a child’s BMI is compared with the CDC growth charts for their exact age and sex, and the result is a percentile. The calculation itself is the same as for adults: weight divided by height squared.
BMI-for-age categories (CDC)
CDC uses the following categories for children and teens aged 2 through 19.
| Category | BMI-for-age percentile |
|---|---|
| Underweight | Below the 5th percentile |
| Healthy weight | 5th to below the 85th percentile |
| Overweight | 85th to below the 95th percentile |
| Obesity | 95th percentile or above |
| Severe obesity | 120% of the 95th percentile or above, or BMI 35 or above |
What BMI can and cannot tell you
BMI is a quick screening measure. It does not distinguish fat from muscle, and children who mature early or play sport can read higher than their body fat would suggest. A pediatrician reads it alongside the child’s growth curve, family history and an examination, and a single measurement says less than the trend across several years.
Which growth charts this uses
This calculator opens on the CDC 2000 BMI-for-age reference, the standard in the United States for ages 2 through 19. Other countries use other charts, and you can switch with the Growth charts menu: the WHO charts (WHO Child Growth Standards under 5, WHO 2007 Growth Reference from 5 to 19) or the Polish OLA and OLAF charts (ages 3 to 18). Each set has its own categories, so the same child can land in a different category on another chart. The BMI-for-age charts start at age 2; younger children’s growth is followed on infant growth charts.
| Chart | Overweight | Obesity | Low BMI |
|---|---|---|---|
| WHO, ages 5 to 19 | Above +1 SD | Above +2 SD | Thinness below -2 SD, severe thinness below -3 SD |
| WHO, under 5 | Above +2 SD (possible risk above +1 SD) | Above +3 SD | Wasted below -2 SD, severely wasted below -3 SD |
| Polish OLAF/OLA, boys | 82.9th centile or above | 97.5th centile or above | Underweight below the 8.4th centile |
| Polish OLAF/OLA, girls | 90.5th centile or above | 98.6th centile or above | Underweight below the 15.8th centile |
Data sources and licences
CDC 2000 BMI-for-age LMS parameters: CDC National Center for Health Statistics (US public domain). WHO tables: World Health Organization, WHO Child Growth Standards (2006) and WHO Growth Reference 2007, reproduced unaltered with attribution. Polish charts: Kułaga Z, Litwin M, Tkaczyk M, et al., “Polish 2010 growth references for school-aged children and adolescents”, European Journal of Pediatrics 2011;170:599-609, licensed CC BY-NC (Creative Commons Attribution Noncommercial), https://pmc.ncbi.nlm.nih.gov/articles/PMC3078309/; and Kułaga Z, Grajda A, Gurzkowska B, et al., “Polish 2012 growth references for preschool children”, European Journal of Pediatrics 2013;172:753-761, licensed CC BY, https://pmc.ncbi.nlm.nih.gov/articles/PMC3663205/. Between ages 6 and 7, which neither Polish table covers, the calculator interpolates between the two.
Frequently asked questions
How is BMI calculated for a child?
The formula is the same as for adults: weight in kilograms divided by height in meters squared (or 703 times weight in pounds divided by height in inches squared). The difference is the interpretation: a child’s BMI is compared with children of the same age and sex and reported as a percentile.
What is a healthy BMI percentile for a child?
CDC classes the 5th to below the 85th percentile as a healthy weight. Below the 5th percentile is underweight, the 85th to below the 95th is overweight, and the 95th or above is obesity.
Why does the calculator ask for months?
The growth charts change month by month, and in young children a few months can move the percentile noticeably. Entering the months since the last birthday gives a more precise result; leaving it at 0 uses the start of that year of age.
Can I use this for an adult or a child under 2?
No. From age 20 the adult BMI categories apply, and the BMI-for-age charts start at age 2. This calculator covers ages 2 through 19 only.
My child’s result is high. What should I do?
Talk with your pediatrician, who will check the measurement, look at the growth chart over time and consider the whole picture. Avoid putting a child on a diet or commenting on their weight without medical advice.
Sources
- CDC. BMI Categories for Children and Teens.
- CDC National Center for Health Statistics. Growth chart data files (BMI-for-age LMS parameters, bmiagerev.csv).
- Kuczmarski RJ, Ogden CL, Guo SS, et al. 2000 CDC Growth Charts for the United States: methods and development. Vital Health Stat 11. 2002;(246):1-190.
- World Health Organization. Growth reference data for 5-19 years: BMI-for-age (expanded tables; interpretation of cut-offs).
- World Health Organization. WHO Child Growth Standards: body mass index-for-age (expanded tables).
- World Health Organization. WHO Child Growth Standards: training course on child growth assessment. Module C, Interpreting growth indicators. Geneva: WHO; 2008.
- Kułaga Z, Litwin M, Tkaczyk M, et al. Polish 2010 growth references for school-aged children and adolescents. Eur J Pediatr. 2011;170(5):599-609. Licence CC BY-NC.
- Kułaga Z, Grajda A, Gurzkowska B, et al. Polish 2012 growth references for preschool children. Eur J Pediatr. 2013;172(6):753-761. Licence CC BY.
- Kułaga Z, Różdżyńska-Świątkowska A, Grajda A, et al. Siatki centylowe dla oceny wzrastania i stanu odżywienia polskich dzieci i młodzieży od urodzenia do 18 roku życia. Standardy Medyczne/Pediatria. 2015;12:119-135.