BMI Calculator
Calculate adult BMI, or use age and sex to estimate BMI-for-age for children and teens.
Adult BMI and BMI-for-age
The BMI formula itself uses only height and weight. For adults aged 20 and older, the standard BMI category does not change according to age or sex. For children and teens aged 2–19, BMI is interpreted using BMI-for-age references that vary by age and sex.
The Child & Teen mode uses CDC 2000 BMI-for-age reference values and estimates between yearly reference points. It is intended for general information and should not replace a clinician's growth-chart assessment.
- Enter the values requested in the calculator.
- Select any units or options that apply.
- Choose Calculate to view the result.
- Use Reset if you want to start again with different values.
Calculation method
The calculator applies the standard relationship shown below.
Results are rounded for readability, so very small rounding differences can occur when compared with manual calculations or other software.
Child and teen BMI categories
For ages 2–19, the category is based on BMI-for-age: below the 5th percentile is underweight, the 5th to below the 85th percentile is healthy weight, the 85th to below the 95th percentile is overweight, and the 95th percentile or above is obesity.
Reference: CDC Growth Charts data files. This calculator provides an educational estimate rather than a clinical diagnosis.
Why this tool is useful
Instead of rebuilding the formula in a spreadsheet or searching for conversion factors, you can enter the values directly and get a consistent result. We keep each tool focused on one task so the inputs and result remain easy to understand on both desktop and mobile screens.
Frequently asked questions
Use the result as a practical estimate or reference. For official, medical, academic, legal or financial decisions, confirm the value with the relevant professional or institution.
This starter version performs calculations in your browser and does not require an account. If you add analytics or advertising later, update the privacy policy to describe the services you actually use.