How this calculator works
The page uses the bundled CDC 2000 LMS reference, interpolating its half-month rows for exact age. It supports a known-BMI input and inverse measurement calculations, and shows reference percentiles for the selected age and chart sex. Those features distinguish it from the general child BMI form. Numerical percentiles outside the central 3rd to 97th range are suppressed; very high BMI needs the CDC extended charts. The age input uses a year of 12 reference months. Inverse results illustrate the equation, not a weight-loss target for a growing teenager. The result is an estimate for information only and is not medical advice.
Formula
BMI = kg / metres²; kg = BMI x metres²; metres = sqrt(kg/BMI). LMS z = ((BMI/M)^L - 1)/(L x S), or ln(BMI/M)/S when L is zero. Reference BMI at z = M x (1 + L x S x z)^(1/L). CDC categories use the 5th, 85th and 95th percentiles.
Worked example
For a boy aged 120.5 months, the CDC median BMI is 16.64613844. At height 1.5 m, weight 37.45381149 kg gives that BMI and the 50th percentile. Entering the same known BMI also gives the 50th percentile.
Advertisement
Frequently asked questions
Why is BMI Prime absent?
Dividing by the adult BMI boundary of 25 is not an age-specific assessment of a teenager. This page uses CDC BMI-for-age comparisons instead.
Are the reference values recommended weights?
No. They describe a growth reference population. A clinician should assess growth over time rather than prescribe a percentile from one measurement.
What changes at age 20?
This teen calculator stops before the 20th birthday. Use an adult BMI tool and appropriate clinical context after that point.