BMI Calculator 2026

According to the CDC and WHO, a healthy BMI range for adults 20 years and older is 18.5 to 24.9. Below 18.5 is classified as underweight, 25.0 to 29.9 is overweight, and 30.0 or above is obese. These ranges are based on large population studies linking BMI to health outcomes. For children and teens (2-19 years), BMI is interpreted using age- and sex-specific percentile charts rather than fixed ranges.

BMI is a useful screening tool for population health but has significant limitations for individuals. It does not distinguish between muscle mass and fat mass, does not account for body composition, and may misclassify certain groups. Athletes with high muscle mass may be classified as overweight or obese despite low body fat. Older adults may have "normal" BMI but high body fat and low muscle mass (sarcopenia). BMI also does not account for fat distribution—abdominal fat is more harmful than subcutaneous fat. For a more complete health assessment, combine BMI with waist circumference, body fat percentage, and other health markers like blood pressure, cholesterol, and blood sugar.

BMR (Basal Metabolic Rate) is the number of calories your body burns at complete rest to maintain basic physiological functions: breathing, circulation, cell production, nutrient processing, and temperature regulation. It accounts for 60-75% of your total daily calorie burn. Our calculator uses the Mifflin-St Jeor equation (1990), which is considered the most accurate BMR formula for the general population: For men: BMR = (10 × weight in kg) + (6.25 × height in cm) - (5 × age in years) + 5. For women: BMR = (10 × weight in kg) + (6.25 × height in cm) - (5 × age in years) - 161. This formula is more accurate than the older Harris-Benedict equation, especially for overweight and obese individuals.

TDEE (Total Daily Energy Expenditure) is your total calorie burn in a day, including BMR plus all activity: physical movement, exercise, digestion (thermic effect of food), and daily tasks. TDEE = BMR × activity multiplier. The standard multipliers are: Sedentary (1.2), Lightly Active (1.375), Moderately Active (1.55), Very Active (1.725), Extra Active (1.9). To lose weight, eat 300-500 calories below TDEE (≈0.5-1 lb/week loss). To gain muscle, eat 300-500 calories above TDEE (≈0.5-1 lb/week gain). To maintain, eat at TDEE. These are starting points—adjust based on actual results over 2-4 weeks.

Our calculator uses the US Navy body fat formula, which estimates body fat percentage from circumference measurements. For men: Body Fat % = 86.010 × log10(waist - neck) - 70.041 × log10(height) + 36.76. For women: Body Fat % = 163.205 × log10(waist + hip - neck) - 97.684 × log10(height) - 78.387. This method is reasonably accurate (±3-4% vs. DEXA scan) when measurements are taken correctly. For best results, measure waist at the navel level, neck at the narrowest point, and hip at the widest point. The Navy method is used by the US military for fitness assessments. For higher accuracy, DEXA scans (±1-2%) or hydrostatic weighing are considered gold standards but require specialized equipment.

According to the American Council on Exercise (ACE), healthy body fat ranges are: For women: Essential fat 10-13%, Athletes 14-20%, Fitness 21-24%, Average 25-31%, Obese 32%+. For men: Essential fat 2-5%, Athletes 6-13%, Fitness 14-17%, Average 18-24%, Obese 25%+. These ranges are higher than BMI classifications because some body fat is essential for health—hormone production, vitamin absorption, organ protection, and temperature regulation. Women naturally carry more essential fat than men due to reproductive biology. Body fat percentages below essential levels can cause health problems including hormone disruption, weakened immunity, and organ damage.