Kids BMI Calculator
Use this kids BMI calculator to estimate your child's BMI percentile for their exact age and sex.
Updated September 18, 2026
Calculated instantly in your browser — nothing is sent to or stored on our servers.
Medical Disclaimer: This calculator provides a general estimate based on established research and is for educational purposes only, not a substitute for medical advice. Individual results can vary based on health conditions, so consult a qualified healthcare professional or registered dietitian before making significant changes to your diet, exercise, or health routine. Read our full Medical Disclaimer.
How Kids BMI Percentile Is Calculated
A child's healthy weight range changes constantly as they grow, which is why children are never assessed against the same fixed BMI cutoffs used for adults. Instead, a child's BMI is compared to a percentile curve built from thousands of other children the same age and sex¹.
What This Calculator Measures
This calculates a child's BMI, then converts it to a percentile against CDC reference data for their exact age and sex, placing them into one of four standard categories rather than a raw number with no context.
The Formula
BMI = weight (kg) ÷ height (m)²
That BMI is then converted to a percentile using the CDC's 2000 growth chart reference data for the child's exact age and sex, not a fixed cutoff table¹.
How This Calculator Computes Your Result
Enter your child's sex, age, height, and weight. We calculate BMI directly, then locate it on the CDC's age- and sex-specific percentile curve to return both the percentile and category.
What the Categories Mean
Underweight (below 5th percentile), Healthy Weight (5th to 85th), Overweight (85th to 95th), Obesity (95th percentile or above).
Why Childhood BMI Percentile Is Tracked at All, Not Just a Snapshot Measure
Childhood BMI percentile isn't just descriptive, it carries real predictive weight for adult outcomes.
A long-term study following children in the Fels Longitudinal Study from childhood into adulthood found that BMI percentile in childhood and adolescence meaningfully predicted the probability of adult overweight and obesity, the higher the childhood percentile and the older the child, the greater the predicted risk of being overweight decades later².
That's part of why pediatric BMI screening exists at all, it isn't just a snapshot of current size, it's tracking a pattern that tends to carry forward, which is also exactly why a single reading matters less than the trend over multiple visits.
A Note on Accuracy
A percentile describes where a child falls relative to a reference population, it is not a diagnosis, and pediatric growth patterns vary widely and normally, especially around puberty. This is a screening reference, not a substitute for a pediatrician's assessment, which considers growth trend over time, not a single measurement.
Frequently Asked Questions
Why doesn't this use the same categories as the adult BMI calculator?
Children are never assessed against fixed BMI cutoffs (18.5/25/30). Their BMI is compared to a percentile curve of children the same age and sex, since healthy body composition changes substantially through growth and puberty.
What do the percentile categories mean?
Underweight is below the 5th percentile, Healthy Weight is 5th to 85th, Overweight is 85th to 95th, and Obesity is at or above the 95th percentile, per CDC convention.
Does childhood BMI percentile actually predict anything about adulthood?
Yes, to a meaningful degree. Long-term tracking of children into adulthood found that higher BMI percentile in childhood and adolescence predicted a higher probability of adult overweight and obesity², which is part of why pediatric screening tracks this over time rather than treating it as a one-time measurement.
Is a single BMI percentile reading concerning on its own?
Not necessarily. Pediatric growth assessment relies heavily on tracking a child's percentile over multiple visits, a single measurement outside an expected range isn't necessarily concerning by itself.
Sources
2000 CDC Growth Charts for the United States: Methods and Development, Kuczmarski, Ogden, Guo et al., National Center for Health Statistics, 2002
Predicting Overweight and Obesity in Adulthood from Body Mass Index Values in Childhood and Adolescence, Guo et al., American Journal of Clinical Nutrition, 2002, Fels Longitudinal Study
Kids BMI Calculator
Use this kids BMI calculator to estimate your child's BMI percentile for their exact age and sex.
Updated September 18, 2026
Calculated instantly in your browser — nothing is sent to or stored on our servers.
Medical Disclaimer: This calculator provides a general estimate based on established research and is for educational purposes only, not a substitute for medical advice. Individual results can vary based on health conditions, so consult a qualified healthcare professional or registered dietitian before making significant changes to your diet, exercise, or health routine. Read our full Medical Disclaimer.
How Kids BMI Percentile Is Calculated
A child's healthy weight range changes constantly as they grow, which is why children are never assessed against the same fixed BMI cutoffs used for adults. Instead, a child's BMI is compared to a percentile curve built from thousands of other children the same age and sex¹.
What This Calculator Measures
This calculates a child's BMI, then converts it to a percentile against CDC reference data for their exact age and sex, placing them into one of four standard categories rather than a raw number with no context.
The Formula
BMI = weight (kg) ÷ height (m)²
That BMI is then converted to a percentile using the CDC's 2000 growth chart reference data for the child's exact age and sex, not a fixed cutoff table¹.
How This Calculator Computes Your Result
Enter your child's sex, age, height, and weight. We calculate BMI directly, then locate it on the CDC's age- and sex-specific percentile curve to return both the percentile and category.
What the Categories Mean
Underweight (below 5th percentile), Healthy Weight (5th to 85th), Overweight (85th to 95th), Obesity (95th percentile or above).
Why Childhood BMI Percentile Is Tracked at All, Not Just a Snapshot Measure
Childhood BMI percentile isn't just descriptive, it carries real predictive weight for adult outcomes.
A long-term study following children in the Fels Longitudinal Study from childhood into adulthood found that BMI percentile in childhood and adolescence meaningfully predicted the probability of adult overweight and obesity, the higher the childhood percentile and the older the child, the greater the predicted risk of being overweight decades later².
That's part of why pediatric BMI screening exists at all, it isn't just a snapshot of current size, it's tracking a pattern that tends to carry forward, which is also exactly why a single reading matters less than the trend over multiple visits.
A Note on Accuracy
A percentile describes where a child falls relative to a reference population, it is not a diagnosis, and pediatric growth patterns vary widely and normally, especially around puberty. This is a screening reference, not a substitute for a pediatrician's assessment, which considers growth trend over time, not a single measurement.
Frequently Asked Questions
Why doesn't this use the same categories as the adult BMI calculator?
Children are never assessed against fixed BMI cutoffs (18.5/25/30). Their BMI is compared to a percentile curve of children the same age and sex, since healthy body composition changes substantially through growth and puberty.
What do the percentile categories mean?
Underweight is below the 5th percentile, Healthy Weight is 5th to 85th, Overweight is 85th to 95th, and Obesity is at or above the 95th percentile, per CDC convention.
Does childhood BMI percentile actually predict anything about adulthood?
Yes, to a meaningful degree. Long-term tracking of children into adulthood found that higher BMI percentile in childhood and adolescence predicted a higher probability of adult overweight and obesity², which is part of why pediatric screening tracks this over time rather than treating it as a one-time measurement.
Is a single BMI percentile reading concerning on its own?
Not necessarily. Pediatric growth assessment relies heavily on tracking a child's percentile over multiple visits, a single measurement outside an expected range isn't necessarily concerning by itself.
Sources
2000 CDC Growth Charts for the United States: Methods and Development, Kuczmarski, Ogden, Guo et al., National Center for Health Statistics, 2002
Predicting Overweight and Obesity in Adulthood from Body Mass Index Values in Childhood and Adolescence, Guo et al., American Journal of Clinical Nutrition, 2002, Fels Longitudinal Study
Kids BMI Calculator
Use this kids BMI calculator to estimate your child's BMI percentile for their exact age and sex.
Updated September 18, 2026
Calculated instantly in your browser — nothing is sent to or stored on our servers.
Medical Disclaimer: This calculator provides a general estimate based on established research and is for educational purposes only, not a substitute for medical advice. Individual results can vary based on health conditions, so consult a qualified healthcare professional or registered dietitian before making significant changes to your diet, exercise, or health routine. Read our full Medical Disclaimer.
How Kids BMI Percentile Is Calculated
A child's healthy weight range changes constantly as they grow, which is why children are never assessed against the same fixed BMI cutoffs used for adults. Instead, a child's BMI is compared to a percentile curve built from thousands of other children the same age and sex¹.
What This Calculator Measures
This calculates a child's BMI, then converts it to a percentile against CDC reference data for their exact age and sex, placing them into one of four standard categories rather than a raw number with no context.
The Formula
BMI = weight (kg) ÷ height (m)²
That BMI is then converted to a percentile using the CDC's 2000 growth chart reference data for the child's exact age and sex, not a fixed cutoff table¹.
How This Calculator Computes Your Result
Enter your child's sex, age, height, and weight. We calculate BMI directly, then locate it on the CDC's age- and sex-specific percentile curve to return both the percentile and category.
What the Categories Mean
Underweight (below 5th percentile), Healthy Weight (5th to 85th), Overweight (85th to 95th), Obesity (95th percentile or above).
Why Childhood BMI Percentile Is Tracked at All, Not Just a Snapshot Measure
Childhood BMI percentile isn't just descriptive, it carries real predictive weight for adult outcomes.
A long-term study following children in the Fels Longitudinal Study from childhood into adulthood found that BMI percentile in childhood and adolescence meaningfully predicted the probability of adult overweight and obesity, the higher the childhood percentile and the older the child, the greater the predicted risk of being overweight decades later².
That's part of why pediatric BMI screening exists at all, it isn't just a snapshot of current size, it's tracking a pattern that tends to carry forward, which is also exactly why a single reading matters less than the trend over multiple visits.
A Note on Accuracy
A percentile describes where a child falls relative to a reference population, it is not a diagnosis, and pediatric growth patterns vary widely and normally, especially around puberty. This is a screening reference, not a substitute for a pediatrician's assessment, which considers growth trend over time, not a single measurement.
Frequently Asked Questions
Why doesn't this use the same categories as the adult BMI calculator?
Children are never assessed against fixed BMI cutoffs (18.5/25/30). Their BMI is compared to a percentile curve of children the same age and sex, since healthy body composition changes substantially through growth and puberty.
What do the percentile categories mean?
Underweight is below the 5th percentile, Healthy Weight is 5th to 85th, Overweight is 85th to 95th, and Obesity is at or above the 95th percentile, per CDC convention.
Does childhood BMI percentile actually predict anything about adulthood?
Yes, to a meaningful degree. Long-term tracking of children into adulthood found that higher BMI percentile in childhood and adolescence predicted a higher probability of adult overweight and obesity², which is part of why pediatric screening tracks this over time rather than treating it as a one-time measurement.
Is a single BMI percentile reading concerning on its own?
Not necessarily. Pediatric growth assessment relies heavily on tracking a child's percentile over multiple visits, a single measurement outside an expected range isn't necessarily concerning by itself.
Sources
2000 CDC Growth Charts for the United States: Methods and Development, Kuczmarski, Ogden, Guo et al., National Center for Health Statistics, 2002
Predicting Overweight and Obesity in Adulthood from Body Mass Index Values in Childhood and Adolescence, Guo et al., American Journal of Clinical Nutrition, 2002, Fels Longitudinal Study