BMI Calculator
Find your Body Mass Index and see the healthy weight range for your height, in seconds.
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Body Mass Index (BMI) is one of the most widely used health screening numbers in the world. It gives you a fast, free snapshot of whether your weight sits in a healthy range for your height, and it is the starting point most doctors and health agencies use before looking deeper.
What is BMI?
BMI is a single number that relates your weight to your height. It was designed as a population screening tool, a quick way to flag people who may be underweight or carrying excess weight and could benefit from a closer look. It does not measure body fat directly, but for most adults it correlates well enough with body fatness to be useful.
How BMI is calculated
The formula is your weight in kilograms divided by the square of your height in meters:
BMI = weight (kg) / height (m)²
In imperial units, it is weight in pounds divided by height in inches squared, multiplied by 703. This calculator converts both for you, so you can enter whichever units you prefer.
How to read your result
Health agencies group adult BMI into four standard categories:
| Category | BMI range |
|---|---|
| Underweight | Below 18.5 |
| Healthy weight | 18.5 to 24.9 |
| Overweight | 25.0 to 29.9 |
| Obesity | 30.0 and above |
Why BMI matters
Across large populations, a higher BMI is linked to a greater risk of conditions such as type 2 diabetes, high blood pressure, heart disease, and some cancers, while a very low BMI carries its own risks. That is why it is used as a first pass. Your individual risk also depends on where you carry fat, your activity, your family history, and your blood markers.
The limits of BMI
BMI has real blind spots. It cannot distinguish muscle from fat, so a lean, muscular athlete can score as overweight. It does not account for sex, age, or ethnicity differences in body composition, and it says nothing about where fat is stored, even though waist fat is more strongly tied to health risk. Treat BMI as one data point, not a diagnosis. Waist circumference and a body fat estimate add valuable context.
What to do with your number
If your BMI is outside the healthy range and you want to change it, the reliable path is a modest, sustained calorie adjustment, enough protein, and consistent physical activity. Crash diets tend to cost muscle and rebound. Small, repeatable habits win. That is exactly what SmaartCoach is built to do: it turns your numbers into a weekly meal plan and a training program, then coaches you through it day by day.
Frequently asked questions
What is a good BMI?
A BMI between 18.5 and 24.9 is considered the healthy range for most adults. Below 18.5 is underweight, 25 to 29.9 is overweight, and 30 or above is in the obese range.
Is BMI accurate for muscular people?
BMI does not tell muscle from fat, so very muscular people can read as overweight while carrying little fat. Pair BMI with a body fat estimate for a fuller picture.
How do I lower my BMI?
BMI drops as weight drops relative to height. A small daily calorie deficit combined with strength training lowers fat while protecting muscle, which is the healthiest way to move your BMI down.
What BMI is used for children?
Children and teens use age and sex specific BMI percentiles, not the adult categories. This calculator is intended for adults 20 and over.
Sources
Reviewed against these authoritative references. Last updated August 2026.
- National Heart, Lung, and Blood Institute (NIH). Calculate Your Body Mass Index
- MedlinePlus, U.S. National Library of Medicine. Body mass index
- World Health Organization. Obesity and overweight (fact sheet)
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