BMI categories for adults
World Health OrganizationRanges apply to most adults aged 20 and over. They are the same for men and women.
What is BMI?
Body Mass Index (BMI) is a simple number that compares your weight to your height. It was developed in the 1830s by Belgian mathematician Adolphe Quetelet and is now used worldwide as a quick screening tool to sort adults into weight categories — underweight, healthy weight, overweight and obese.
The formula is straightforward:
BMI = weight (kg) ÷ height (m)²
Because it needs only two measurements that almost anyone can take at home, BMI is a practical first check on whether your weight might be affecting your health. It does not measure body fat directly, but for most people it tracks closely enough to be useful at a population level.
What BMI does not tell you
BMI is a screening tool, not a diagnosis. It has real limitations you should keep in mind:
- It can’t tell muscle from fat. A muscular athlete can have a “high” BMI while carrying very little fat.
- It ignores where fat sits. Fat around the waist is more strongly linked to health risk than fat on the hips — waist circumference adds useful information.
- It varies by population. Some ethnic groups face higher health risk at a lower BMI, so cut-offs are sometimes adjusted.
- It isn’t for everyone. Children, pregnant people and frail older adults need different measures.
Treat your BMI as one data point. If it falls outside the healthy range, it’s a prompt to look closer — ideally with a doctor — not a verdict.
Know your calories next
BMI tells you where you stand today. Our calorie calculator tells you how much to eat to get where you want to go — maintenance, cutting or bulking, with a macro breakdown.
Open the Calorie CalculatorCommon questions
What is a healthy BMI?
For most adults a BMI between 18.5 and 24.9 is considered healthy. Below 18.5 is underweight, 25–29.9 is overweight, and 30 or above is classed as obese.
How is BMI calculated?
Divide your weight in kilograms by your height in metres squared (kg/m²). In imperial units, multiply weight in pounds by 703, then divide by your height in inches squared.
Is BMI accurate for everyone?
No single number fits everyone. BMI doesn’t separate muscle from fat, so athletes, pregnant people and older adults may need extra measures like waist circumference or a body-fat scan.
Does BMI work for children?
Not the adult version. Children and teens are assessed with age- and sex-specific BMI percentiles. This calculator is intended for adults aged 20 and over.