Why age matters for BMI
For adults, a BMI of 24 means the same thing whether you are 25 or 65 - the
categories are fixed. Age still matters for interpretation, because
muscle and fat naturally shift over the years, but it does not move the
boundaries. For children and teens it is different: they are still growing,
so a healthy BMI range depends on both age and sex and is expressed as a
percentile rather than a fixed category.
Adult BMI categories (ages 20+)
Adult BMI categories for ages 20 and older | Category | BMI range |
| Underweight | Below 18.5 |
| Healthy Weight | 18.5 - 24.9 |
| Overweight | 25.0 - 29.9 |
| Obesity | 30.0 and above |
| Class 1 Obesity | 30.0 - 34.9 |
| Class 2 Obesity | 35.0 - 39.9 |
| Class 3 Obesity | 40.0 and above |
Children and teens (ages 2-19)
Instead of the adult bands, a child's BMI is compared with growth charts to
produce a percentile - for example, the 60th percentile means a higher BMI
than 60% of children of the same age and sex. Because that comparison
requires official reference data, we point you to the CDC Child and Teen BMI
Calculator for the percentile category, and provide a safe BMI number on our
child BMI calculator page.
What your result means
Whether you are an adult or looking up a child's figure, BMI is a screening
measure, not a diagnosis. It is a useful prompt to talk with a healthcare
provider, who can factor in age, growth, history, and other measurements.
Frequently asked questions
Does BMI change by age?
For adults 20 and older, the BMI categories stay the same regardless of age - a BMI of 24 means the same thing at 25 as it does at 65. Age still matters for interpretation, because muscle and fat distribution change over time. For children and teens 2-19, BMI must be read against age- and sex-specific growth charts instead of adult categories.
Why is a child's BMI handled differently?
Children and teens are still growing, so a healthy BMI range changes with age and differs between boys and girls. Instead of fixed adult categories, child BMI is interpreted using BMI-for-age percentiles from growth charts. This page can calculate the BMI number, but the official percentile category should come from the CDC Child and Teen BMI Calculator.
Is there a different BMI calculator for women by age?
Adult BMI categories do not change for women by age, so the same calculator works whether you are 25 or 70. We include an optional age field because many people search for a calculator that lets them enter it, and because age is useful background when you discuss your result with a clinician.
Is a BMI calculator accurate?
A BMI calculator accurately reports the BMI number for the height and weight you enter. As a health measure, BMI is a useful screening tool for populations, but it has limits for individuals: it does not separate muscle from fat and does not account for where fat is stored. It is best used as a quick check, not a diagnosis.
How do you use this BMI calculator?
Choose US units or metric units with the toggle, enter your height and weight, optionally add age and sex for context, then select Calculate. Your BMI and adult category appear instantly. Nothing you type is sent anywhere - the calculation happens entirely in your browser.