What Is BMI?

Body Mass Index (BMI) is a numerical value calculated from your weight and height. It provides a quick screening tool to categorize individuals into weight categories: underweight, normal weight, overweight, and obese.

The formula is straightforward: BMI = weight (kg) ÷ height (m)². For example, a person weighing 70 kg and standing 1.75 m tall has a BMI of 22.9, which falls in the normal range.

BMI Categories

BMI Range	Category
Below 18.5	Underweight
18.5 – 24.9	Normal weight
25.0 – 29.9	Overweight
30.0 – 34.9	Obese Class I
35.0 – 39.9	Obese Class II
40.0+	Obese Class III

Limitations of BMI

While BMI is widely used and easy to calculate, it has significant limitations. It does not distinguish between muscle mass and fat mass. Athletes and highly muscular individuals may have a high BMI despite having low body fat. Similarly, older adults who have lost muscle mass may have a normal BMI but carry excess fat.

For a more complete picture of your body composition, consider using our Body Fat Calculator alongside your BMI. Waist circumference and waist-to-hip ratio are also valuable metrics that BMI alone cannot capture.

BMI and Health Risk

Research shows that BMI values outside the normal range (18.5–24.9) are associated with increased health risks. A BMI above 30 is linked to higher rates of cardiovascular disease, type 2 diabetes, hypertension, and certain cancers. However, BMI is a population-level screening tool, not a diagnostic measure — your overall health depends on many factors including diet quality, physical activity, sleep, and genetics.

Using BMI for Weight Goals

Your BMI can help you set realistic weight targets. The calculator shows your healthy weight range based on your height. If your BMI indicates you are overweight, even a modest weight loss of 5-10% of your body weight can significantly improve health markers. Use our Calorie Deficit Calculator to plan a safe, sustainable timeline for reaching your target weight.

BMI for Different Populations

BMI thresholds may vary for different ethnic groups. The WHO suggests that Asian populations may face health risks at lower BMI values, with overweight classified at 23 and obesity at 27.5. For children and adolescents, BMI is interpreted using age-specific and sex-specific percentile charts rather than fixed categories.

Next step: Your BMI is a starting point. For a complete picture, calculate your TDEE to understand your daily calorie needs, then use the Macro Calculator to plan your nutrition.

Frequently Asked Questions

BMI is a useful screening tool but not a definitive measure of health. It does not account for muscle mass, bone density, age, sex, or fat distribution. Use it as one data point alongside body fat percentage, waist circumference, and clinical health markers.

A BMI between 18.5 and 24.9 is considered healthy for most adults. This range is associated with the lowest risk of weight-related health conditions. However, optimal BMI can vary based on age, sex, ethnicity, and muscle mass.

Yes. BMI does not differentiate between muscle and fat. Athletes, bodybuilders, and people with high muscle mass may have a BMI over 25 while having low body fat and excellent cardiovascular health. In these cases, body fat percentage is a better metric.

The same BMI scale is used for both sexes, but women naturally carry more body fat than men at the same BMI. A woman with a BMI of 24 typically has more body fat than a man with the same BMI. This is one reason why body fat percentage provides a more nuanced picture.

Checking your BMI once a month is sufficient for tracking trends. If you are actively working on weight loss or muscle building, focus more on body composition changes (measurements, body fat %) rather than BMI alone, as muscle gain can increase BMI even while you are losing fat.

For imperial units: BMI = (weight in pounds × 703) ÷ (height in inches)². For example, a person weighing 154 lbs and standing 5'9" (69 inches) has a BMI of 22.7. Our calculator handles the conversion automatically.

BMI Calculator