BMI Calculator.
Know your number.
Calculate your Body Mass Index instantly. See your category, healthy weight range, and what it means. Free, no signup required.
What this calculator does
BMI (Body Mass Index) is a simple ratio of weight to height. This tool estimates your BMI, shows the usual WHO category bands, and gives a rough healthy weight range for your height.
- Inputs: height, weight, age, and sex (age and sex help frame context in the explanations below).
- Limitations: BMI does not measure body fat directly. Athletes with high muscle mass, older adults, and some ethnic groups may be misclassified. Use it as a screening number, not a diagnosis.
- Who it is for: adults looking for a quick screening metric. For children, BMI is interpreted with growth charts, not this adult calculator.
Best next step after BMI is setting a practical intake target. Use the calorie deficit calculator, check maintenance in the TDEE calculator, and read our weight loss guide for context.
Medical disclaimer: LeanCalc does not provide medical advice. Talk to a healthcare professional before changing diet or exercise.
<18.5 Healthy
18.5 to 24.9 Overweight
25 to 29.9 Obese
30+
Calculate your exact calorie deficit and macro targets to reach your goal weight.
Try the Calorie Deficit Calculator →BMI categories explained
| BMI Range | Category | Health risk |
|---|---|---|
| Below 18.5 | Underweight | Increased risk of malnutrition |
| 18.5 to 24.9 | Healthy weight | Lowest health risk |
| 25.0 to 29.9 | Overweight | Moderate increased risk |
| 30.0 to 34.9 | Obese (Class I) | High risk |
| 35.0 to 39.9 | Obese (Class II) | Very high risk |
| 40.0+ | Obese (Class III) | Extremely high risk |
How is BMI calculated?
BMI (Body Mass Index) is calculated by dividing your weight in kilograms by the square of your height in metres: BMI = kg ÷ m².
For imperial units: BMI = (weight in lbs × 703) ÷ (height in inches)².
For example: a person who is 175 cm tall and weighs 75 kg has a BMI of 75 ÷ (1.75)² = 24.5, which falls in the healthy range.
Is BMI accurate?
BMI is a useful and widely-used screening tool, but it has limitations. It does not account for muscle mass, bone density, age, sex, or where fat is distributed on the body. Athletes with high muscle mass may have a high BMI despite being very healthy. Older adults may have a normal BMI but carry excess body fat.
Use BMI as a starting point alongside other measures like waist circumference, body fat percentage, and advice from a healthcare provider.
Frequently asked questions
What is a healthy BMI for women?
The healthy BMI range of 18.5 to 24.9 applies to adult women and men. However, research suggests women tend to carry more body fat than men at the same BMI, so some guidelines use slightly different thresholds by sex.
Does BMI change with age?
The standard BMI scale is designed for adults aged 18 to 65. For children and teenagers, BMI is assessed differently using percentile charts that account for age and sex. For older adults, a slightly higher BMI (around 25 to 27) may be associated with better outcomes.
What should I do if my BMI is too high?
A BMI above 25 suggests carrying excess weight. The most effective approach is a moderate calorie deficit combined with regular physical activity. Use our Calorie Deficit Calculator to find your daily target.