# BMI Calculator — Free BMI Calculator for Women & Men > Free BMI calculator for women and men. Calculate your Body Mass Index instantly > and get your healthy weight range, BMI Prime, and evidence-based tips — fast, > free, no sign-up. All calculations run locally in your browser. Canonical page: https://bmicalculatorsystem.com/ ## What BMI actually tells you Body Mass Index is a screening measure that relates your weight to your height. It is not a diagnosis — it is a fast, free signal that correlates with body fatness and disease risk at the population level. - **A screening tool, not a verdict.** BMI flags whether your weight is likely in a healthy zone for your height. Doctors use it as a starting point, then look at waist size, blood work, and history. - **Risk rises at both ends.** Being under 18.5 carries its own serious risks, from weakened immunity to osteoporosis. - **The sweet spot is 21–23.** Within the 18.5–24.9 healthy band, large studies associate a BMI around 21–23 with the lowest all-cause mortality for most adults. ## BMI categories ### Adults (20+) — WHO | BMI (kg/m²) | Category | | ------------- | ----------------- | | < 16.0 | Severe thinness | | 16.0 – 16.9 | Moderate thinness | | 17.0 – 18.4 | Mild thinness | | 18.5 – 24.9 | Normal weight | | 25.0 – 29.9 | Overweight | | 30.0 – 34.9 | Obese — Class I | | 35.0 – 39.9 | Obese — Class II | | ≥ 40.0 | Obese — Class III | ### Children & teens (2–19) — CDC percentiles | Percentile | Category | | ---------------------- | --------------- | | < 5th percentile | Underweight | | 5th – 84th percentile | Healthy weight | | 85th – 94th percentile | Overweight | | ≥ 95th percentile | Obesity | Children and teens use the same formula, but the result is interpreted with age- and sex-specific percentiles from CDC growth charts. A healthy weight sits between the 5th and 85th percentile. ## The formulas ``` # Metric BMI = weight_kg / height_m² # US units BMI = 703 × weight_lb / height_in² # Derived metrics BMI_Prime = BMI / 25 Ponderal_Index = weight_kg / height_m³ # Healthy weight range for your height min_weight = 18.5 × height_m² max_weight = 24.9 × height_m² ``` Every result is computed locally in your browser with these exact formulas. Nothing is uploaded, logged, or stored. ## Health risks at both ends **BMI above 25:** high blood pressure; type 2 diabetes and insulin resistance; coronary heart disease and stroke; high LDL cholesterol and triglycerides; sleep apnea; osteoarthritis; certain cancers (endometrial, breast, colon); gallbladder disease. **BMI below 18.5:** malnutrition and vitamin deficiencies; weakened immune function; osteoporosis and fracture risk; anemia and fatigue; fertility and hormonal issues; growth and development delays (in youth); surgical complications; muscle wasting (sarcopenia). ## How to improve your BMI, sustainably - **Eat in a small deficit, not a crash diet.** A 300–500 kcal daily deficit produces steady loss of about 0.5 kg per week. - **Prioritise protein and fibre.** Protein (1.2–1.6 g per kg of body weight) preserves muscle while losing fat and keeps you full. - **Move 150 minutes a week, minimum.** The WHO baseline is 150–300 minutes of moderate activity weekly. - **Lift something twice a week.** Resistance training 2+ days per week preserves lean mass and raises resting energy expenditure. - **Sleep 7–9 hours.** Short sleep disrupts hunger hormones and increases intake. - **Track trends, not days.** Weigh in weekly under the same conditions and judge the 4-week trend. - **Underweight? Gain deliberately.** Add 300–500 kcal/day from energy-dense whole foods paired with resistance training. - **Get a professional in the loop.** If your BMI is below 18.5 or above 30, see a doctor or registered dietitian. ## Where BMI falls short - **Muscle vs. fat:** BMI cannot tell them apart; athletes often score "overweight." - **Fat distribution:** Visceral (belly) fat is far riskier than fat elsewhere — pair BMI with a waist measurement. - **Age & sex:** Older adults and women carry more fat at the same BMI; cut-offs do not adjust for either. - **Ethnicity:** Risk rises at lower BMIs for some Asian populations — the WHO suggests action points of 23 and 27.5 instead of 25 and 30. ## BMI for women A BMI calculator for women uses exactly the same formula and 18.5–24.9 healthy range. What differs is interpretation: at the same BMI, women naturally carry more body fat than men. BMI is **not valid during pregnancy or breastfeeding**. After menopause, fat shifts toward the abdomen, so pair BMI with a waist measurement (ideally under 80 cm / 31.5 in). ## BMI for men A BMI calculator for men applies the same formula and ranges, but more muscle mass means BMI more often overstates body fat. Risk rises meaningfully above a waist of 94 cm (37 in) and sharply above 102 cm (40 in). A high BMI plus a high waist measurement is a genuine signal worth acting on; a high BMI with a lean waist usually is not. ## FAQ **What is a good BMI score?** For most adults, a BMI between 18.5 and 24.9 is the healthy range per the WHO. A BMI of roughly 21–23 is associated with the lowest health risk for many populations. **How is BMI calculated?** Weight in kilograms divided by height in metres squared (kg/m²). In US units: 703 × weight in pounds divided by height in inches squared. **Is the BMI calculation different for women and men?** No — the formula and the 18.5–24.9 healthy range are identical for both sexes. Only interpretation differs. **Is BMI accurate for athletes?** Not always. BMI cannot distinguish muscle from fat, so muscular people often score as "overweight" while carrying little body fat. **Does BMI work for children and teenagers?** Ages 2–19 use the same formula, but results use age- and sex-specific CDC percentiles. Healthy weight is the 5th–85th percentile. **What is BMI Prime?** Your BMI divided by 25. Below 1 means within or under the healthy range; above 1 means you exceed it (e.g. 1.10 = 10% over). **How fast can I safely change my BMI?** A safe, sustainable rate is 0.5–1 kg (1–2 lb) per week through a moderate calorie deficit and regular activity. --- This site provides general health information, not medical advice. Always consult a healthcare professional.