BMI Calculator
Check your Body Mass Index instantly. Enter your height and weight to see your BMI score, category, and what it means for your health.
Your details
Fill in your details to see your BMI score and category.
Track client progress inside HubFit
Monitor weight, body metrics, and progress photos for every client from one coaching platform.
Explore HubFit →How to Use This BMI Calculator
Using this calculator takes seconds. Select your preferred unit system (Metric or Imperial), enter your age, gender, height, and weight, and your BMI will be calculated instantly. The result shows your BMI score, which category you fall into, and a colour-coded scale so you can see exactly where you stand. BMI works as a quick screening tool: it gives you a single number that summarises the relationship between your height and weight.
What is BMI?
Body Mass Index (BMI) is a simple formula that divides your weight in kilograms by the square of your height in metres: BMI = weight (kg) / height (m)^2. It was developed in the early 19th century by Belgian mathematician Adolphe Quetelet and is now used globally by healthcare systems as a quick screening tool for weight-related health risks. While it cannot measure body fat directly, BMI is a useful starting point for understanding whether your weight falls into a range associated with higher or lower health risks.
Understanding Your BMI Category
A BMI under 18.5 is classified as underweight, which can indicate insufficient nutrition or an underlying health condition. A BMI between 18.5 and 24.9 is considered normal weight and is associated with the lowest risk of weight-related health problems. A BMI of 25 to 29.9 is overweight, and a BMI of 30 or above falls into the obese range, which is further divided into three classes. Each step up in BMI category is associated with an increased risk of conditions like type 2 diabetes, cardiovascular disease, and joint problems.
Limitations of BMI
BMI does not distinguish between muscle and fat. A muscular athlete may have a high BMI but very low body fat, while an older adult with significant muscle loss could have a normal BMI but a high body fat percentage. BMI also does not account for where your body stores fat: abdominal fat (visceral fat) carries greater health risks than fat stored on the hips or thighs. For a more complete picture, consider pairing your BMI result with a body fat percentage measurement and waist circumference.
BMI for Different Populations
Standard BMI categories were developed using data from European and North American populations. Research shows that health risks may occur at lower BMI thresholds for people of South Asian, East Asian, and Southeast Asian descent. Some health organisations use adjusted cut-offs for these populations, with overweight starting at 23 and obesity at 27.5. Age also matters: older adults may benefit from a slightly higher BMI (25 to 27) as a buffer against muscle loss and frailty.
What to Do With Your Results
If your BMI falls outside the normal range, use it as a prompt to look deeper rather than a definitive diagnosis. Pair it with other measurements like body fat percentage, waist-to-hip ratio, and blood work. If your goal is to move into a healthier BMI range, a modest calorie deficit of 300 to 500 calories per day combined with resistance training is the most sustainable approach. Recalculate your BMI every 4 to 6 weeks to track your progress over time.
Frequently asked questions.
Supercharge your coaching business
See why HubFit is the coaching platform of choice for modern fitness professionals.