UNDERSTAND THE METHOD
How to use this calculator
Select adults or children and teens. Enter weight and standing height. For a child or teen, also enter the source sex category and completed age in years and additional months. The calculation adds half a month to the completed month. Adult results use fixed BMI categories; child results use the CDC age-specific reference.
What the result can tell you
BMI is a screening measure and is not a diagnosis or a direct body-fat measurement. Children need age-specific references. The CDC reference here covers 24 to less than 240 months. Children younger than 2 need WHO growth standards. The chart version and age assumption stay with the result.
Common questions
How do I enter a child or teen age?
Enter completed years and additional completed months. The calculator adds half a month to that age to use the midpoint of the completed month.
Can I use the child reference for a child younger than 2?
No. This CDC reference covers 24 to less than 240 months. Children younger than 2 need the applicable WHO growth standards.
Sources & limitations
Sources checked September 12, 2026. These notes identify methods and assumptions. They have not received an independent clinical review.
- CDC adult BMI categories apply from age 20.cdc.gov
- Official CDC LMS data support BMI-for-age calculations.cdc.gov
- The 2022 CDC extension describes upper-tail BMI percentiles.cdc.gov
- CDC documents completed-month ages and extended BMI calculations.cdc.gov