Free adult BMI calculator
Your BMI, with the context.
Body mass index (BMI) compares weight with height. Calculate it, then see what it leaves out.
Start with height and weight
For adults 20 and older; not for use during pregnancy. Use the CDC child and teen calculator for ages 2–19.
Your measurements and result stay in this page. We do not save them or send them to analytics. No account or email required.
When to skip this calculator
Do not use this tool during pregnancy, if a condition affects your height, or if you have or think you may have an eating disorder. A health professional can help choose a more appropriate assessment. You can read the guide without entering measurements.
This tool uses the CDC adult age range of 20 and older. Its input limits help catch unit mistakes; they are not targets for height or weight.
A number. Then a clearer picture.
What will the result tell me?
You’ll see your calculated BMI, its standard adult category, and the calculation behind it. Then explore what that number leaves out.
BMI compares weight with height. It cannot separate muscle, fat and bone, or show where body fat is carried.
You can use the fictional example if you would rather explore without entering your own measurements.
A useful question for your next visit
“How does BMI fit with my blood pressure, lab results, medical history and what matters to me?”
Build an appointment question list →What the categories mean
These standard CDC categories apply to adults 20 and older. Category boundaries are screening cutoffs, not sudden changes in someone’s health.
| Category | BMI (kg/m²) |
|---|---|
| Underweight | Below 18.5 |
| Healthy weight | 18.5 to below 25 |
| Overweight | 25 to below 30 |
| Obesity | 30 or above |
Within the obesity category: class 1 is 30 to below 35; class 2 is 35 to below 40; class 3 is 40 or above.
Keep the whole person in view
BMI is useful for screening, but a full assessment also considers medical history, daily habits, physical examination and laboratory findings. Two people with the same BMI can have different body composition and health circumstances.
Read what BMI can and cannot tell you →Explore health measures beyond weight →Sources & scope
General education, not a diagnosis or a treatment recommendation. Sources checked October 26, 2026.
- CDC: BMI formulas and limitations
- CDC: Adult BMI categories
- CDC: BMI and individual health
- CDC: Adult calculator and input ranges
- NHS: When a BMI calculator may not be appropriate (UK guidance; this tool uses CDC’s US adult categories and age range).