This BMI for Age for Men Calculator uses the CDC growth chart LMS method to convert a boy’s height and weight (or a direct BMI) into an age-adjusted BMI percentile and z-score. Because body composition changes rapidly during childhood and adolescence, raw BMI alone is misleading for males under 20 — this tool places each measurement on the correct percentile curve for the child’s exact age in months.
Use it to screen for underweight, healthy weight, overweight, and obesity using the standard CDC categories (underweight <5th, healthy 5th–84th, overweight 85th–<95th, obesity ≥95th). The reverse mode works the other way: enter a target percentile (e.g., the 85th) and the calculator returns the BMI value that corresponds to that percentile at the given age — useful for setting weight goals or interpreting research thresholds.
The calculator accepts ages from 24 to 240 months (2–20 years) and lets you enter weight in kg or lb, height in cm, m, in, or ft. Results include the BMI, z-score, percentile, and a color-coded weight category, plus a step-by-step breakdown of the LMS calculation.
📅 Age
⚖️ Weight
📏 Height
How to Use This Tool
Enter the boy’s age in years and months (2–20 years), then choose a mode. In Standard mode, input weight and height (with units) to get the BMI, percentile, and z-score. In Reverse mode, enter a target percentile to find the BMI that corresponds to that percentile at the given age. Use the preset buttons for quick fills, then click Calculate.
Age in months matters. The CDC LMS tables are indexed by month. A 10-year-old at 120 months and at 130 months will have different percentile curves, so always include the month value for accuracy.
How It Works
The calculator uses the CDC growth chart LMS method. For each age, three parameters are defined: L (power transformation), M (median BMI), and S (coefficient of variation). The z-score is computed as:
z = [(BMI/M)L − 1] / (L × S) (for L ≠ 0)
The percentile is then obtained from the standard normal cumulative distribution. In reverse mode, the inverse normal CDF (Acklam’s algorithm) converts a percentile to a z-score, and the BMI is solved from the LMS equation. Values are linearly interpolated between the 6-month CDC reference points.
Worked Examples
Example 1: A 10-year-old boy (120 months) weighs 45 kg and is 150 cm tall. BMI = 45 / (1.5)² = 20.0 kg/m². Using the LMS parameters at 120 months (L ≈ −2.806, M ≈ 15.424, S ≈ 0.123), the z-score is about 0.92, placing him at the 82nd percentile — healthy weight.
Example 2: For a 16-year-old (192 months), what BMI corresponds to the 95th percentile? With L ≈ −2.612, M ≈ 16.129, S ≈ 0.129 and z = 1.645, the BMI ≈ 26.1 kg/m². Any value above this would be classified as obesity.
Tips & Best Practices
- Use a calibrated scale and a stadiometer for height; self-reported values can shift percentiles by several points.
- For clinical decisions, always plot the result on the official CDC growth chart and consider trends over time.
- The reverse mode is handy for setting weight goals: find the BMI at the 85th percentile, then work backward to a target weight.
Limitations
This tool is designed for males aged 24–240 months. It does not apply to adults (BMI categories differ) or to females (separate LMS tables). The LMS values are rounded to 6-month intervals; interpolation gives results within about 1 percentile point of the full CDC data. Always confirm with the official CDC charts for clinical use.
Reference: CDC BMI-for-Age LMS Table (Males, selected ages)
| Age (months) | L | M (median BMI) | S |
|---|---|---|---|
| 24 | −1.650 | 15.959 | 0.097 |
| 60 | −3.236 | 15.275 | 0.116 |
| 120 | −2.806 | 15.424 | 0.123 |
| 180 | −2.624 | 15.989 | 0.128 |
| 240 | −2.570 | 16.790 | 0.136 |
Frequently Asked Questions
Why can’t I use adult BMI categories? Adult cutoffs (25 and 30) assume a stable body composition, but children and teens grow at different rates. The percentile approach accounts for age and sex.
What does the z-score mean? The z-score is the number of standard deviations from the median. A z-score of +2 corresponds to roughly the 97.7th percentile.
Is this tool a medical diagnosis? No. It is an educational screening aid. Consult a pediatrician for a full evaluation.
For the official CDC data, see the CDC Growth Chart Data Files.