BMI Calculator

BMI is a widely used measurement that relates your weight to your height, offering a general indicator of whether you’re in a healthy weight range for your height

In the metric system: BMI = weight (kg) ÷ [height (m)]². In U.S. customary units: BMI = 703 × weight (lbs) ÷ [height (in)]²

The categories are ranges defined (for adults) by organisations such as World Health Organization (WHO) or the Centers for Disease Control and Prevention (CDC) that group BMI values into classifications like underweight (<18.5), normal (18.5–25), overweight (25–30), and obese (>30).

Being underweight can carry health risks including malnutrition, vitamin deficiencies, anemia, weakened immune function, osteoporosis, growth and development issues (especially in children/teens) and, for women, potential reproductive complications

Excess weight increases the risk of high blood pressure, elevated “bad” cholesterol (LDL), type 2 diabetes, heart disease, stroke, gallbladder disease, sleep apnea, certain cancers, joint problems (such as osteoarthritis), and generally a reduced quality of life and increased mortality, according to a study in The Lancet

BMI is a useful screening tool but it’s not perfect. It does not directly measure body fat, muscle mass, bone density or fat distribution. For example:

- A very muscular athlete might score as “overweight” by BMI despite low body fat.


- Older adults may have higher body fat for the same BMI as younger adults.


- BMI may be less accurate for children, teens, and some ethnic groups

Yes, with caution. For ages about 2–20, BMI is compared to age- and sex-specific percentiles (e.g., underweight if <5th percentile, healthy 5th-85th, at risk 85th-95th, overweight >95th) rather than the fixed adult categories.

No. BMI is a starting point. It provides a quick estimate of where you stand relative to general height-weight norms. But for a full assessment, clinical factors like body composition (fat-vs-muscle), waist circumference, blood pressure, metabolic markers and lifestyle need to be considered.

If your BMI falls into the underweight or overweight/obese category, it may be a good idea to talk with a healthcare provider. Together you can evaluate whether there are underlying causes (e.g., nutrient deficiency, hormonal, metabolic) and discuss a safe, personalised plan to move toward a healthier weight.

For most people, checking it once in a while (for example, every few months) is sufficient, especially if you are actively making lifestyle changes. More frequent checks might make sense if you’re following a medical or weight-management programme. But always remember: the number is less important than how you feel, your health markers and sustainable habits.

Not always. The “normal” adult BMI range (18.5-25 kg/m²) is commonly used but different countries and populations may use adjusted cut-offs. Also, what is “healthy” depends on individual factors including age, sex, ethnicity, muscle mass and overall health profile.

 • Waist circumference (abdominal fat is a major risk factor)
 • Body composition (fat percentage vs muscle)
 • Blood pressure, cholesterol, glucose levels
 • Physical fitness (strength, endurance, flexibility)
 • Sleep, stress, nutrition, physical activity habits
 BMI is useful, but the broader picture matters more.

Not necessarily. It depends on your situation. If you’re underweight due to illness, recovery or nutrient deficiency, weight gain may be needed. If overweight, improving diet quality, increasing physical activity and metabolic health may matter just as much as the number on the scale. A healthcare professional can help tailor the right strategy for you.

Pregnancy and breastfeeding introduce physiological changes (fluid shifts, foetal growth, etc) that make BMI less reliable. Similarly, for bodybuilders or those with very high muscle mass, BMI may over-estimate body fat. In such cases, other measures or professional assessment may be more appropriate.