Free calculators
Body mass index (BMI) calculator
Enter a few details to see your BMI, category, and a healthy weight range for your height.
What is BMI?
Body mass index (BMI) compares your weight to your height. It is a screening number — not a diagnosis — that groups people as underweight, healthy weight, overweight, or obese. Doctors, researchers, and health apps use it because it is simple, cheap, and works at a population level.
How this BMI calculator works
We use the standard adult formula: BMI = weight (kg) ÷ height (m)². Sex and age do not change the number for adults; they help you read the result in context. You can enter metric (cm, kg) or imperial (ft/in, lb) units — we convert behind the scenes.
BMI categories
For adults, the World Health Organization classifies BMI as underweight below 18.5, healthy from 18.5 to 24.9, overweight from 25.0 to 29.9, and obese at 30.0 or above. These cut-offs are the same for women and men. Children and teens need age-specific charts, so treat youth results as a rough signal only.
How to read your result
A BMI in the healthy band is a useful target for many people, but it is not the whole story. Muscle is denser than fat, so athletes can land in overweight while being metabolically healthy. Abdominal fat is more strongly linked to disease than fat on the hips or thighs. Use BMI together with waist size, energy, blood work, and how your clothes fit.
Limits of BMI
BMI does not measure body fat, bone density, or where you carry weight. It can overestimate risk in muscular people and underestimate it in people with little muscle. Older adults often do better with a slightly higher BMI than young adults. If you are pregnant, have an eating disorder, or a medical condition that affects weight, skip the number and speak with a clinician.
What is a healthy BMI?+
For most adults, a BMI between 18.5 and 24.9 is classed as a healthy weight. That range is a guide, not a personal prescription.
Does a high BMI always mean I am unhealthy?+
No. BMI cannot see muscle versus fat. Strength athletes often have a high BMI with low body fat. The reverse can also be true: a “normal” BMI with little muscle and a large waist.
How often should I check my BMI?+
A few times a year is enough for most people. Day-to-day weight noise (salt, food in the gut, hormones) moves the number more than fat does. Weekly weigh-ins in an app are more useful than chasing BMI daily.
Put the numbers into practice
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