BMI Calculator
Body Mass Index with visual health gauge
What is BMI?
Body Mass Index (BMI) is a measurement using height and weight to estimate whether you are at a healthy weight. It is calculated by dividing weight in kilograms by height in meters squared.
BMI Categories
| BMI Range | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 - 24.9 | Normal weight |
| 25.0 - 29.9 | Overweight |
| 30.0+ | Obese |
Limitations
BMI does not distinguish between muscle and fat mass and may not be accurate for athletes, elderly individuals, or pregnant women. Consult a healthcare professional for a complete assessment.
Important health note
This calculator is for general information and self-checking only. It should not be used as a diagnosis, treatment plan, or replacement for advice from a qualified doctor, dietitian, trainer, or other healthcare professional. If you are pregnant, managing a medical condition, taking medication, recovering from illness, or making a major diet or exercise change, please speak with a professional before acting on the result.
A better way to read your BMI result
BMI is useful as a quick screening number, but it should not be treated as a full health report. Muscle mass, body composition, age, pregnancy, and medical conditions can all change how the result should be interpreted. Use it as a starting point, then compare it with waist measurement, daily activity, and advice from a qualified health professional when needed.
BMI Calculator: practical guide
The BMI Calculator is built for people who want a fast answer without losing context. It keeps the calculation simple, shows the result clearly, and helps you understand what the number means before you use it in a real decision.
BMI compares your weight with your height to give a simple weight-status indicator. It is useful for population-level screening and for personal tracking, but it should be read alongside body composition, waist size, medical history, and fitness level.
What is the best way to use the BMI Calculator?
Enter the values carefully, review the units, and use the result as a reliable reference point. The BMI Calculator is most useful when you compare scenarios or repeat the calculation with consistent inputs.
Is the BMI Calculator accurate?
The calculator follows standard calculation logic, but accuracy depends on the values you enter and the assumptions behind the formula. For important health decisions, use it as guidance and verify the result with a trusted source.
What is BMI and how is it calculated?
Body Mass Index (BMI) is a numerical value calculated from your height and weight. It is used as a screening tool to classify individuals into weight categories that may indicate health risks. The formula divides weight in kilograms by height in metres squared.
BMI Formula: BMI = Weight (kg) ÷ Height² (m²)
Example: A person weighing 70 kg and 1.75 m tall has a BMI = 70 ÷ (1.75 × 1.75) = 70 ÷ 3.0625 = 22.9 — which falls in the Normal range.
BMI categories for adults
The World Health Organization (WHO) defines the following BMI ranges for adults aged 18 and over:
- Below 18.5 — Underweight: May indicate malnutrition, eating disorders, or other health conditions
- 18.5 – 24.9 — Normal weight: Associated with the lowest risk of weight-related health problems
- 25.0 – 29.9 — Overweight: Increased risk of cardiovascular disease, type 2 diabetes, and hypertension
- 30.0 – 34.9 — Obese Class I: High risk of metabolic and cardiovascular conditions
- 35.0 – 39.9 — Obese Class II: Very high risk
- 40.0 and above — Obese Class III (Severe): Extremely high health risk
BMI for men vs women
The BMI formula is the same for men and women, but the health implications differ slightly. Women naturally carry more essential body fat (approximately 10–13%) compared to men (2–5%) due to hormonal and reproductive functions. This means a woman with the same BMI as a man may have a different body fat percentage. Despite this, WHO uses the same BMI ranges for both sexes in adult classification.
BMI for different age groups
For adults aged 18–65, the standard WHO ranges apply. For children and teenagers, BMI is interpreted differently using age- and sex-specific percentile charts rather than fixed category ranges. For adults over 65, a slightly higher BMI (25–27) may be considered acceptable as some additional weight can be protective in older age.
Limitations of BMI
BMI is a useful population-level screening tool but has important limitations for individuals:
- Does not measure body fat directly — a muscular athlete can have a high BMI but very low body fat
- Does not account for fat distribution — visceral fat around organs is more dangerous than subcutaneous fat under the skin, but BMI cannot distinguish between them
- Varies by ethnicity — Asian populations have higher health risks at lower BMI values; WHO recommends lower thresholds (23 for overweight, 27.5 for obese) for Asian adults
- Does not reflect muscle mass — bodybuilders often register as obese by BMI despite very low body fat
For a more complete health picture, combine BMI with waist circumference measurement and, where possible, body fat percentage assessment.
Healthy BMI ranges by age (adults)
- 18–24 years: 18.5–24.9 (standard range)
- 25–34 years: 18.5–24.9 (standard range)
- 35–44 years: 18.5–24.9 (standard range)
- 45–54 years: 18.5–24.9 (standard range)
- 55–65 years: 18.5–24.9 (standard range); some guidelines accept up to 27 for older adults
- 65+ years: 22–27 considered acceptable by many geriatric guidelines
Frequently asked questions about BMI
Is BMI accurate for everyone? BMI is a population screening tool, not a diagnostic measure for individuals. It works reasonably well for most sedentary adults but is less reliable for athletes, elderly individuals, pregnant women, and certain ethnic populations.
What is a healthy BMI for a woman? For adult women, a BMI between 18.5 and 24.9 is considered the normal healthy range. For South and East Asian women, a lower threshold of 23 is often recommended due to higher metabolic risk at lower BMI values.
Can I have a normal BMI but still be unhealthy? Yes. This is called "normal weight obesity" — where someone has a normal BMI but an unhealthy proportion of body fat, especially visceral fat. Waist circumference above 80 cm for women or 94 cm for men indicates elevated risk regardless of BMI.
How do I lower my BMI? BMI decreases when body weight decreases relative to height. A combination of a moderate calorie deficit (300–500 calories below TDEE), adequate protein intake (1.6–2 g per kg of bodyweight), and regular physical activity produces sustainable BMI reduction.
Related health calculators
Use these tools alongside your BMI for a more complete health assessment: