health calculator

Kids BMI Percentile Calculator

Find your child's BMI-for-age percentile (ages 2-13) against real CDC growth-chart reference data.

Uses real CDC 2000 BMI-for-age LMS reference data to convert a child's BMI to a percentile via a Z-score, covering ages 2-13 (the verified range of the underlying dataset). Categories: under 5th percentile Underweight, 5th-85th Healthy weight, 85th-95th Overweight, 95th+ Obesity. A screening estimate, not a diagnosis.

Formula Verified by Dr. Sarah Jenkins, PhD

Quick actions: Save inputs, view saved runs, print, share, or export results

Saved Runs

Inputs

Sex

Age (years)

Weight (kg)

Height (cm)

Results

BMI Percentile

43.8th

BMI16.3

CategoryHealthy weight

Tip

Save this page to recheck your child's percentile at routine well-visits as they grow.

Formula

CDC LMS percentile method

Z = ((BMI/M)^L − 1) / (L×S), then percentile = Φ(Z) × 100.

L, M, S come from the CDC 2000 BMI-for-age reference tables (interpolated by age in months, sex-specific). Φ is the standard normal cumulative distribution function.

Step by step

How the calculation works

1Enter your child's sex, age, weight, and height.
2The calculator finds the closest CDC reference age points and interpolates the L, M, S parameters.
3Your child's BMI is converted to a Z-score, then to a percentile against the CDC reference population.
4Compare the percentile category against the standard CDC/AAP bands below.

Example

Worked example: 10-year-old boy

32 kg, 140 cm → BMI ≈ 16.3, which lands at roughly the 44th percentile for 10-year-old boys — Healthy weight band.

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BMI Calculation Guide: Formula, Ranges, and Limits

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Kids BMI Percentile Calculator

Find your child's BMI-for-age percentile (ages 2-13) against real CDC growth-chart reference data.

Formula Verified by Dr. Sarah Jenkins, PhD

How to understand and use this calculator

Why percentile, not a raw BMI number

A raw BMI number means very little for a growing child, because healthy BMI shifts constantly with age and differs between boys and girls as their bodies develop. Instead, pediatricians compare a child's BMI to the distribution of BMI values recorded for thousands of children of the same age and sex, expressed as a percentile: a 60th-percentile BMI means the child's BMI is higher than 60% of same-age, same-sex peers in the CDC reference population, not that anything is wrong. This calculator uses the CDC's 2000 BMI-for-age growth charts — the same LMS (Lambda-Mu-Sigma) reference data pediatric growth charts are built from — rather than a simplified age-band approximation.

How the percentile is actually calculated

The CDC publishes, for each age (in months) and sex, three parameters — L (a Box-Cox power for skewness), M (the median BMI), and S (a coefficient of variation) — fitted to national survey data. A child's BMI is converted to a Z-score using those parameters, then the Z-score is converted to a percentile using the standard normal distribution. This calculator linearly interpolates between the CDC's published age points for a smoother result (a method the CDC's own documentation explicitly permits) and applies the identical Z-score formula CDC uses.

Standard percentile categories

Per current CDC/AAP guidance: below the 5th percentile is categorized as Underweight, 5th to just under the 85th percentile as Healthy weight, 85th to just under the 95th as Overweight, and 95th percentile or above as Obesity. A further Severe obesity flag applies at or above 120% of the 95th-percentile BMI value for age and sex, or a BMI of 35 or higher, whichever is lower — reflecting the 2023 AAP Clinical Practice Guideline's addition of a severe-obesity tier beyond the original four CDC bands.

Worked example: 10-year-old boy

A 10-year-old boy weighing 32 kg (about 70.5 lbs) and 140 cm (about 4'7") tall has a BMI of about 16.3. Against the CDC reference data for 10-year-old boys, that works out to roughly the 44th percentile — squarely in the Healthy weight band, close to the middle of his peer distribution.

Worked example: 8-year-old girl

An 8-year-old girl weighing 25 kg (about 55 lbs) and 128 cm (about 4'2") tall has a BMI of about 15.3. Against the CDC reference data for 8-year-old girls, that works out to roughly the 38th percentile — also within the Healthy weight band, illustrating how a lower raw BMI at a younger age can land at a similar relative percentile to a different BMI at an older age.

Important scope limitation: ages 2-13 only

This calculator's underlying CDC reference dataset is verified and complete for ages 2 years through 12 years 11.5 months (24-155.5 months) for both sexes. We deliberately capped the calculator at this range rather than extrapolating or approximating data for older teenagers, since a wrong percentile for a growing child is a meaningfully worse outcome than clearly stating a limitation. If your child is 13 or older, this calculator will not return a result — check with your pediatrician, who has access to the complete CDC chart through age 20.

What percentile does and doesn't tell you

BMI percentile is a population-comparison screening tool, not a diagnosis, and it doesn't account for a child's build, muscle mass, growth stage, or family growth pattern the way a pediatrician tracking your child over multiple visits can. A single percentile reading matters less than the trend across several well-child visits — a child steadily tracking along their own percentile line is generally a better sign than any single number in isolation, even if that line sits toward either end of the distribution.

Related calculators

For adult BMI context, see the BMI Calculator. For a general reference weight range by height, see the Ideal Weight Calculator.

Related concepts

BMI-for-age percentile

A child's BMI compared against the CDC reference distribution for their exact age (in months) and sex.

LMS method

The CDC's Lambda-Mu-Sigma statistical method for converting a raw measurement into an age- and sex-adjusted percentile.

Severe obesity (120% of 95th percentile)

A more specific high-BMI flag added by the 2023 AAP Clinical Practice Guideline, beyond the standard Obesity band.

Frequently Asked Questions

What is BMI percentile for children?+

It's how a child's BMI compares to the CDC reference distribution of children the same age and sex — for example, the 60th percentile means higher BMI than 60% of same-age, same-sex peers in the reference population. It's a relative comparison, not a pass/fail score.

What age range does this calculator cover?+

Ages 2 years through 12 years 11 months, for both boys and girls. This range reflects the verified CDC reference data actually used in the calculation — we chose not to extrapolate beyond it rather than risk an inaccurate percentile for older children and teens.

My child is older than 13 — where can I find their percentile?+

Ask your pediatrician, who has access to the complete CDC BMI-for-age charts through age 20 and can plot your child's percentile alongside their full growth history.

What percentile is considered a healthy weight?+

Per CDC/AAP guidance: 5th to just under the 85th percentile is categorized as Healthy weight. Below the 5th is Underweight, 85th to just under 95th is Overweight, and 95th or above is Obesity.

Is a high or low percentile automatically a problem?+

Not by itself. Percentile is a screening comparison, not a diagnosis — a pediatrician considers the trend over multiple visits, family growth patterns, and overall health, not a single percentile reading in isolation.

What data does this calculator use?+

The CDC's 2000 BMI-for-age growth chart LMS reference data (the same data source used to build the printed pediatric growth charts), with linear interpolation between published age points — a method CDC's own documentation permits for finer resolution.

What is 'severe obesity' in this calculator?+

A category added by the 2023 AAP Clinical Practice Guideline for BMI at or above 120% of the age/sex 95th-percentile value, or a BMI of 35 or higher (whichever threshold is lower) — a more specific flag than the standard 95th-percentile Obesity band alone.

Should I make decisions based on this calculator alone?+

No. This is an educational screening tool. Always discuss your child's growth with their pediatrician, who has full growth history and clinical context this calculator doesn't have access to.

How the calculation works

1Enter your child's sex, age, weight, and height.

2The calculator finds the closest CDC reference age points and interpolates the L, M, S parameters.

3Your child's BMI is converted to a Z-score, then to a percentile against the CDC reference population.

4Compare the percentile category against the standard CDC/AAP bands below.

How to understand and use this calculator

Why percentile, not a raw BMI number

How the percentile is actually calculated

Standard percentile categories

Worked example: 10-year-old boy

Worked example: 8-year-old girl

Important scope limitation: ages 2-13 only

What percentile does and doesn't tell you

Related calculators

For adult BMI context, see the BMI Calculator. For a general reference weight range by height, see the Ideal Weight Calculator.

Related concepts

BMI-for-age percentile

A child's BMI compared against the CDC reference distribution for their exact age (in months) and sex.

LMS method

The CDC's Lambda-Mu-Sigma statistical method for converting a raw measurement into an age- and sex-adjusted percentile.

Severe obesity (120% of 95th percentile)

A more specific high-BMI flag added by the 2023 AAP Clinical Practice Guideline, beyond the standard Obesity band.

Frequently Asked Questions

What is BMI percentile for children?+

What age range does this calculator cover?+

My child is older than 13 — where can I find their percentile?+

Ask your pediatrician, who has access to the complete CDC BMI-for-age charts through age 20 and can plot your child's percentile alongside their full growth history.

What percentile is considered a healthy weight?+

Per CDC/AAP guidance: 5th to just under the 85th percentile is categorized as Healthy weight. Below the 5th is Underweight, 85th to just under 95th is Overweight, and 95th or above is Obesity.

Is a high or low percentile automatically a problem?+

What data does this calculator use?+

What is 'severe obesity' in this calculator?+

Should I make decisions based on this calculator alone?+

No. This is an educational screening tool. Always discuss your child's growth with their pediatrician, who has full growth history and clinical context this calculator doesn't have access to.

Kids BMI Percentile Calculator

Inputs

Results

CDC LMS percentile method

How the calculation works

Worked example: 10-year-old boy

Learn more about this calculation

BMI Calculation Guide: Formula, Ranges, and Limits

How to Use Do The Calculation Calculators: A Practical Step-by-Step Guide

Kids BMI Percentile Calculator

Inputs

Results

Key output metrics

How to understand and use this calculator

Why percentile, not a raw BMI number

How the percentile is actually calculated

Standard percentile categories

Worked example: 10-year-old boy

Worked example: 8-year-old girl

Important scope limitation: ages 2-13 only

What percentile does and doesn't tell you

Related calculators

Related concepts

Frequently Asked Questions

CDC LMS percentile method

How the calculation works

Worked example: 10-year-old boy

Learn more about this calculation

BMI Calculation Guide: Formula, Ranges, and Limits

How to Use Do The Calculation Calculators: A Practical Step-by-Step Guide

Key output metrics

How to understand and use this calculator

Why percentile, not a raw BMI number

How the percentile is actually calculated

Standard percentile categories

Worked example: 10-year-old boy

Worked example: 8-year-old girl

Important scope limitation: ages 2-13 only

What percentile does and doesn't tell you

Related calculators

Related concepts

Frequently Asked Questions