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Body mass index (BMI) calculator
Enter a few details to see your BMI, category, and a healthy weight range for your height.
Written by Robert Winter · Published August 17, 2026 · Last reviewed August 23, 2026
Editorial standardsWhat 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 screening 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. WHO and CDC materials note that extra fat around the waist is more strongly linked to disease risk than BMI alone, which is why waist size is often used alongside BMI. Some observational research finds older adults may have lower mortality at a slightly higher BMI; that is context, not a reason to gain weight. 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. It is a population screening tool, not a personal diagnosis. 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.
Primary sources
Health facts on this page are tied to these public-health and peer-reviewed sources. Product notes about Pureo are our own.
- Obesity and overweight fact sheet — World Health Organization
- A healthy lifestyle — WHO recommendations — World Health Organization
- Adult BMI categories — Centers for Disease Control and Prevention
- BMI calculator and healthy weight — National Health Service (UK)
- Assessing your weight — Centers for Disease Control and Prevention
How Pureo tests this
We use the standard adult BMI formula and the WHO, CDC, and NHS adult category bands. Sex and age do not change the number. We re-check the cut-offs against those agency pages when we edit this calculator. BMI is a screening estimate, not a diagnosis.
Read our editorial standardsNot medical advice. This page is general information. It is not a diagnosis, treatment plan, or personal medical advice. Talk to a qualified clinician before changing how you eat, especially if you are pregnant, have an eating disorder, or have a medical condition that affects weight.
Put the numbers into practice
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