BMI Calculator

The WHO defines a healthy BMI as 18.5–24.9 for adults of European descent. For Asian populations, the WHO recommends lower thresholds: overweight at ≥23, obese at ≥27.5, due to higher metabolic risk at lower BMI values. These are screening ranges — individual health should be assessed alongside other clinical markers.

BMI (kg/m²) = weight in kilograms ÷ (height in metres)². For imperial units: BMI = 703 × weight (lbs) ÷ height (inches)². For example, a person weighing 75 kg at 1.75 m tall: BMI = 75 ÷ (1.75²) = 75 ÷ 3.0625 = 24.5.

No. BMI is a poor indicator for highly muscular individuals. Since muscle is denser than fat, an athlete may have a high BMI (e.g., 27–30) while having low body fat (10–15%). For athletes, body fat percentage measured by DEXA or hydrostatic weighing is a more meaningful assessment.

The WHO classifies BMI ≥30 as obese, further divided into Class I (30–34.9), Class II (35–39.9), and Class III or "morbidly obese" (≥40). Each class carries progressively higher risk of type 2 diabetes, cardiovascular disease, certain cancers, and all-cause mortality.

Yes, but differently. For children and teens (2–19 years), BMI is plotted against age- and sex-specific growth charts (CDC or WHO). The result is expressed as a BMI-for-age percentile rather than an absolute value. Below the 5th percentile is underweight; 85th–95th is overweight; above the 95th is obese.

Yes. People of Asian descent have higher body fat percentages at the same BMI as white European populations, and experience metabolic complications (insulin resistance, type 2 diabetes) at lower BMI values. WHO recommends: Asian overweight ≥23, obese ≥27.5. Some guidelines also recommend lower thresholds for South Asian, Chinese, and Japanese populations.

BMI prime is BMI divided by the upper limit of the normal BMI range (25). A BMI prime <0.74 is underweight, 0.74–0.99 is normal, 1.0–1.19 is overweight, and ≥1.2 is obese. It allows easy comparison across different BMI scales and is especially useful for comparing Asian and European thresholds.

By WHO classification, yes — BMI 25.0–29.9 is classified as "overweight." However, BMI 25 represents the upper boundary of the normal range and carries only a modestly increased risk compared to 24.9. Population studies consistently show that mortality risk begins to meaningfully increase above BMI 27–28 rather than precisely at 25.

Elevated BMI (≥25, particularly ≥30) is associated with increased risk of: type 2 diabetes, cardiovascular disease (coronary artery disease, heart failure, stroke), certain cancers (breast, colon, endometrial, kidney), obstructive sleep apnoea, osteoarthritis, non-alcoholic fatty liver disease, and all-cause mortality. Risk increases progressively with BMI class.

Underweight (BMI <18.5) is associated with: malnutrition and micronutrient deficiencies, impaired immune function, osteoporosis and fracture risk, anaemia, infertility, poor wound healing, and increased all-cause mortality. In younger individuals, low BMI may indicate eating disorders that require specialist intervention.

A normal BMI (18.5–24.9) corresponds to a weight range that depends on your height. For example, at 170 cm, the normal weight range is approximately 53.5–72 kg (118–159 lbs). Use our calculator above to find your specific healthy weight range.

Waist circumference and waist-to-height ratio may be stronger predictors of metabolic disease risk than BMI because they better reflect abdominal visceral fat, which is more metabolically active than subcutaneous fat. WHO recommends action at waist circumference ≥94 cm (men) / ≥80 cm (women). Using both BMI and waist circumference together is more informative than either alone.

The concept of "metabolically healthy obesity" is debated in the literature. Some individuals with BMI ≥30 have normal blood pressure, blood glucose, cholesterol, and insulin sensitivity. However, long-term prospective studies suggest that metabolically healthy obesity is often a transitional state — many individuals develop metabolic abnormalities over time. BMI alone does not determine health.

Body composition shifts with age: lean muscle mass decreases (sarcopenia) while fat mass tends to increase, particularly centrally. This means an older adult may have a "normal" BMI while having excess fat and low muscle mass — a condition called "sarcopenic obesity." For adults over 65, some research suggests a slightly higher "optimal" BMI (22–27) is associated with better outcomes, possibly due to metabolic reserves.

The Ponderal Index (PI) = weight (kg) ÷ height³ (m³). It was proposed as an improvement on BMI because taller people tend to have higher BMI values simply due to height scaling. PI may be a better predictor of body fatness in very tall or very short individuals. However, it has less population-level validation than BMI and is rarely used in clinical practice.

For most adults maintaining a stable weight, checking every few months is sufficient. If you're actively losing or gaining weight, monthly recalculation gives a clearer trend without overreacting to daily fluctuations from water weight, food volume, or hormonal cycles. BMI is a slow-moving metric — day-to-day weight swings of 1–2 kg are normal and don't reflect real changes in body composition.

BMI only accounts for total weight relative to height — it cannot distinguish between muscle, fat, bone density, or fluid. Two people at the same height and BMI can have very different body fat percentages, muscle mass, and frame sizes. This is why BMI is best used as a population-level screening tool rather than a precise individual diagnostic — waist circumference, body fat %, or a simple mirror/photo comparison over time often tell you more about your specific body.

No — standard BMI categories do not apply during pregnancy, since weight gain (fetus, placenta, amniotic fluid, increased blood volume, and fat stores) is expected and healthy. Instead, clinicians use pre-pregnancy BMI to guide recommended total weight gain ranges (e.g., roughly 11.5–16 kg for a pre-pregnancy BMI in the normal range, per Institute of Medicine guidelines) and track gain against trimester-specific curves rather than applying adult BMI categories directly.

Only by losing weight generally, and BMI can't tell you what kind of weight you lost. Losing muscle (from severe calorie restriction without resistance training, or from illness) would also lower BMI while worsening body composition and metabolic health. This is one of BMI's key limitations — a falling number isn't automatically a win unless it's coming primarily from fat loss, which BMI alone cannot confirm.

The formula itself is identical, but interpretation shifts with age. Some geriatric research suggests a BMI of 22–27 (slightly above the standard "normal" ceiling of 24.9) is associated with better survival outcomes in adults over 65, likely reflecting greater metabolic and muscle reserves during illness. This doesn't mean higher BMI is universally better in older age — it means the standard young-adult cutoffs are a less precise fit, and a geriatrician's assessment carries more weight than the number alone.

BMI is a simple ratio of weight to height and takes seconds to calculate with no equipment beyond a scale and tape measure. Body fat percentage measures the actual proportion of your body that is fat mass versus lean mass (muscle, bone, organs, water), typically via DEXA scan, skinfold calipers, or bioelectrical impedance. Body fat % is more physiologically meaningful but requires equipment and is harder to measure accurately at home — which is why BMI remains the standard first-pass screening tool despite its limitations.

Genetics influence body weight regulation, fat distribution, and metabolic rate, and a family history of obesity is associated with higher lifetime risk. However, this affects your risk context, not the BMI number or formula itself — the same BMI thresholds and health-risk associations apply. Knowing your family history is more useful for motivating earlier, proactive lifestyle habits and closer monitoring of blood sugar and blood pressure than for reinterpreting the BMI calculation.

Not necessarily. The normal BMI range (18.5–24.9) spans a fairly wide weight window for any given height, and where you sit within it — along with muscle mass, fitness level, waist circumference, and lab markers like blood pressure and cholesterol — matters more for individual health than simply landing inside the range. Someone at the low end of "normal" with little muscle and someone at the high end with strong muscle mass and good fitness can have very different actual health profiles despite similar BMI.

It's a reasonable starting reference point — the normal BMI range for your height gives you a sensible ballpark — but it shouldn't be the only factor. A better approach is to combine a BMI-informed range with how you feel, your energy levels, strength and fitness markers, waist circumference trends, and guidance from a healthcare provider, rather than fixating on hitting one exact number on a formula that doesn't know your muscle mass or frame size.