Body Mass Index (BMI) Calculator
This calculator provides estimates for educational purposes only and is not medical advice. Results may vary based on individual factors. Consult a healthcare provider before making changes to your diet or exercise routine.
What is BMI?
Body Mass Index (BMI) is a measure that uses your height and weight to estimate whether you are at a healthy weight. It is calculated by dividing your weight in kilograms by your height in meters squared. Doctors and health organizations worldwide use BMI as a quick screening tool, though it works best alongside other measurements.
BMI Categories
- Underweight: BMI < 18.5
- Normal: BMI 18.5 - 24.9
- Overweight: BMI 25.0 - 29.9
- Obesity: BMI ≥ 30.0
BMI limitations
BMI is a useful starting point, but it has blind spots. It cannot tell the difference between muscle and fat — a lean, muscular person may register as "overweight" while someone with low muscle mass and higher body fat could show as "normal." Age, gender, and ethnicity also influence what a healthy weight looks like.
For a more complete picture, consider checking your body fat percentage or using our Ideal Body Weight Calculator which compares four published formulas (Devine, Robinson, Miller, and Hamwi) to give you a realistic target weight range.
What to do with your result
If your BMI is outside the normal range, the next step is understanding your calorie needs. Our Daily Calorie Intake Calculator shows how many calories you need to maintain, lose, or gain weight based on your activity level. For a structured approach to reaching a healthier weight, try the Weight Loss Calculator — it builds a personalized timeline with milestones so you can track progress week by week.
Frequently asked questions
What is BMI?
Body Mass Index (BMI) is a numerical value calculated from your weight and height. It provides a simple screening measure to categorize you as underweight, normal weight, overweight, or obese.
How is BMI calculated?
BMI is calculated by dividing your weight in kilograms by the square of your height in meters (kg/m²). For example, a person who weighs 70 kg and is 1.75 m tall has a BMI of 22.9.
What is a healthy BMI range?
A BMI between 18.5 and 24.9 is generally considered healthy for adults. Below 18.5 is underweight, 25-29.9 is overweight, and 30 or above is classified as obese.
Is BMI accurate for athletes?
BMI does not distinguish between muscle and fat. Athletes or people with high muscle mass may have a high BMI while being perfectly healthy. For a more complete picture, use a body fat percentage measurement alongside BMI.
Does BMI change with age?
The BMI formula itself does not change with age for adults, but healthy ranges may shift slightly. Older adults may carry a slightly higher BMI without increased health risk. Children and teens use age-specific BMI percentile charts.
Formulas and scientific references Body mass index (Quetelet index): weight in kg divided by height in metres squared, classified against the WHO adult cut-offs. There is no sex or age correction - BMI is defined the same way for every adult.
Sources
- World Health Organization BMI classification for adults (underweight below 18.5, healthy weight 18.5-24.9, overweight 25.0-29.9, obesity from 30.0). World Health Organization, Nutrition Landscape Information System
This calculator gives a general educational estimate, not medical or individualized nutrition advice. Prediction equations are wrong by more than 10% in roughly 1 in 3 people.