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BMI Calculator

Calculate your Body Mass Index by age and gender. Understand what your BMI really means for your health — beyond the number — with personalized analysis.

What Is BMI and How Is It Calculated?

Body Mass Index (BMI) is a simple screening tool that divides your weight in kilograms by the square of your height in metres. A result below 18.5 is considered underweight, 18.5 to 24.9 is normal, 25 to 29.9 is overweight, and 30 or above is classified as obese. Healthcare providers use BMI as a first-pass indicator of potential weight-related health risks such as heart disease, type 2 diabetes, and joint problems. While BMI is quick and free to calculate, it does not directly measure body fat, so it should be combined with other assessments for a complete picture of your health.

Is BMI Accurate for Athletes and Muscular People?

BMI has a well-known limitation: it cannot distinguish between lean muscle mass and body fat. A muscular athlete with low body fat may register an overweight or even obese BMI purely because muscle is denser than fat. For this reason, strength athletes, bodybuilders, and anyone who carries significant muscle mass should pair BMI with a body fat percentage measurement. Methods like the Navy body fat formula, skinfold calipers, or DEXA scans provide a much clearer view of body composition. BMI remains useful for the general population, but context matters when interpreting results.

Frequently Asked Questions

What is a healthy BMI?▼
A healthy BMI generally falls between 18.5 and 24.9 for adults. However, the ideal range can shift slightly depending on your age, sex, and ethnic background. Older adults may tolerate a slightly higher BMI without added health risk, while certain populations face elevated risk even within the normal range.
Why is BMI not accurate for athletes?▼
BMI uses only height and weight, so it cannot differentiate between muscle and fat tissue. An athlete with heavy lean muscle may have a high BMI despite having a low body fat percentage. Supplementing BMI with body fat measurements or a DEXA scan gives a far more accurate health assessment.
What is the difference between BMI and body fat percentage?▼
BMI is a ratio of weight to height and does not measure fat directly. Body fat percentage tells you exactly how much of your total weight is fat tissue. Two people with the same BMI can have very different body fat levels depending on their muscle mass and overall body composition.

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