BMI Calculator
Body Mass Index — based on WHO & NIH international standards. Works for adults 18–65.
<18.5 Normal
18.5–24.9 Overweight
25–29.9 Obese
≥30
What is BMI and How is it Calculated?
Body Mass Index (BMI) is a numerical value derived from a person's weight and height. The formula is: BMI = weight (kg) ÷ height² (m²). It was developed by Belgian mathematician Adolphe Quetelet in the 1830s and is widely used as a screening tool by the World Health Organization (WHO).
While BMI is a useful starting point for assessing weight categories, it does not directly measure body fat or account for muscle mass, bone density, age, sex, or ethnicity. Athletes may have a high BMI due to muscle, while older adults may have a normal BMI but still carry excess body fat.
| BMI Range | Category | Health Risk |
|---|---|---|
| Below 18.5 | Underweight | Malnutrition, osteoporosis risk |
| 18.5 – 24.9 | Normal weight | Lowest health risk |
| 25.0 – 29.9 | Overweight | Moderate risk of metabolic disease |
| 30.0 – 34.9 | Obese Class I | High risk |
| 35.0 – 39.9 | Obese Class II | Very high risk |
| 40.0+ | Obese Class III | Extremely high risk |
Calorie Calculator (TDEE)
Calculate your Total Daily Energy Expenditure using the Mifflin-St Jeor equation — the gold standard used by dietitians worldwide.
Understanding TDEE and Calorie Needs
Your Total Daily Energy Expenditure (TDEE) is the total number of calories your body burns in a day, accounting for your Basal Metabolic Rate (BMR) plus activity. The Mifflin-St Jeor equation, adopted in 2005 by the American Dietetic Association, is considered the most accurate for most people.
BMR Formulas Used: Male: (10 × weight kg) + (6.25 × height cm) − (5 × age) + 5. Female: (10 × weight kg) + (6.25 × height cm) − (5 × age) − 161. Your TDEE is your BMR multiplied by your activity factor.
Body Fat % Calculator
Uses the US Navy circumference method — one of the most accurate non-invasive body composition measurements available.
Ideal Weight Calculator
Calculates ideal weight using 5 different medical formulas — Hamwi, Devine, Robinson, Miller, and BMI range.
Daily Water Intake Calculator
Calculate optimal hydration based on your weight, activity level, and climate. Based on EFSA and IOM guidelines.
Macro Nutrients Calculator
Get your daily protein, carbs, and fat targets based on your goal, bodyweight, and activity. Used by fitness coaches and nutritionists.
Disclaimer & Medical Notice
All calculators on WellnessCalculators.com are for informational and educational purposes only. Results are estimates based on established medical formulas (Mifflin-St Jeor, WHO BMI standards, US Navy body fat method) and should not be used as a substitute for professional medical advice, diagnosis, or treatment.
Always consult with a qualified healthcare provider, registered dietitian, or certified fitness professional before making significant changes to your diet, exercise, or health regimen. Individual results may vary based on genetics, medical history, and other factors.