BMI-for-age for women is a growth-based interpretation of body mass index used for females from age 2 through 20. Instead of applying fixed adult cutoffs, it places a girl's BMI on a percentile curve from the CDC 2000 growth charts. That percentile shows how her body mass compares with same-age female peers and is the basis for underweight, healthy weight, overweight, and obesity categories during childhood and adolescence.
This BMI-for-age calculator takes age, height, and weight in either metric or imperial units. It calculates BMI, estimates the BMI-for-age percentile using LMS curve data, and reports the corresponding weight-status category. It also gives a healthy weight range for the entered height, which is useful for screenings, school health assessments, and parent-teacher discussions.
Results are educational estimates for screening purposes only. They do not replace a pediatrician, family doctor, or registered dietitian's growth evaluation.
📊 Your Results
Quick Start Guide
Enter the girl's age in years (2 to 20; decimals are fine), then height and weight in either metric or imperial units. The unit dropdowns let you switch between centimeters, meters, inches, and feet for height, and kilograms or pounds for weight. Press Calculate to see BMI, approximate BMI-for-age percentile, weight-status category, and a healthy weight range for that height. Press Reset to clear all fields.
- Use measured height and weight when possible.
- For a single screening, use the most recent measurements.
- For growth tracking, calculate at regular intervals and record the percentile each time.
How BMI-for-Age Is Calculated
First, BMI is calculated from weight and height: BMI = weight in kilograms divided by height in meters squared. For BMI-for-age, this BMI value is then transformed into a z-score using LMS parameters from growth charts. M is the median BMI at that age, L is a skewness correction, and S is the coefficient of variation. The z-score formula is z = (((BMI / M)^L) - 1) / (L × S), and the z-score is converted to a percentile using the standard normal distribution. Our calculator uses a compact yearly LMS table for females ages 2-20 and linearly interpolates between whole-year values for decimal ages.
The CDC publishes clinical growth charts with exact percentile curves; see the CDC clinical growth charts for reference.
Worked Examples
Example 1: An 8-year-old girl is 130 cm tall and weighs 32 kg. Height in meters = 1.30 m, so BMI = 32 ÷ (1.30 × 1.30) = 18.9 kg/m². Using the approximate age-8 LMS values, this is roughly the 89th percentile, which falls in the overweight category.
Example 2: A 15-year-old girl is 165 cm tall and weighs 56 kg. BMI = 56 ÷ (1.65 × 1.65) = 20.6 kg/m². The approximate percentile is about 44th, which is a healthy weight status.
Example 3: A 5-year-old girl is 110 cm tall and weighs 19 kg. BMI = 19 ÷ (1.10 × 1.10) = 15.7 kg/m², close to the age-5 median, so her percentile is about 50th.
Interpreting the Percentile Categories
For females ages 2-20, the CDC classifies weight status by BMI-for-age percentile. The percentile reflects where the BMI falls on a reference distribution, not a direct percentage of body fat.
| Percentile Range | Weight Status |
|---|---|
| Less than 5th | Underweight |
| 5th to less than 85th | Healthy weight |
| 85th to less than 95th | Overweight |
| 95th and above | Obese |
Limitations and Factors That Affect Accuracy
This tool uses a simplified yearly LMS interpolation rather than the exact monthly CDC LMS datasets, so percentiles are close estimates rather than official clinical values. BMI-for-age does not directly measure body fat. A muscular teenager can have a high BMI with a healthy body composition, while another teen with a normal BMI may still have excess fat. The timing of puberty also affects BMI, so a percentile can shift during adolescence. The tool is intended for females ages 2-20; for younger children, the WHO Child Growth Standards are more appropriate, and for adult women the fixed adult BMI categories are the standard.
- Birth to 2 years: use WHO growth standards.
- Ages 2-20: use BMI-for-age percentiles.
- Ages 20 and older: use adult BMI cutoffs.
- Always interpret growth measurements in context, not in isolation.
Frequently Asked Questions
Why is BMI-for-age not used for adult women? After linear growth stops, the age-related BMI curves flatten, and fixed adult BMI categories are more practical. Adult BMI does not depend on age because body size relative to height has stabilized after growth is complete.
What if the age is older than 20? This calculator is intentionally limited to ages 2-20. For adult women, use a standard BMI calculator and apply the general adult categories.
Can I track growth with one measurement? One measurement gives a point-in-time percentile, but growth trends over several visits are much more informative. A child who holds near the same percentile over time is usually growing consistently.
Does this calculator diagnose obesity? No. It is a screening estimate. A pediatrician or qualified health professional should confirm any weight-related concern with a full assessment.
Are these exact CDC percentiles? The results are based on a simplified yearly LMS table with linear interpolation and are meant for general education. For clinical decisions, use the official CDC growth charts or clinical software with the full monthly LMS data.