Free Health Calculator – BMI, Calorie, BMR, Body Fat, Age & More

Health Calculator — Science-Based Tools for Better Wellness

CalcHub's health calculator collection brings together six essential wellness metrics into one easy-to-use suite. Using established medical formulas and WHO guidelines, these tools give you accurate, personalized health data instantly — with no personal data stored, no account needed, and no subscriptions required. Whether you're starting a fitness journey, monitoring progress, or simply curious about your health numbers, these calculators provide the insight you need.

All formulas used are peer-reviewed and widely accepted in medical and fitness communities. We use the Mifflin-St Jeor equation for calorie estimation (the most accurate for most individuals), the WHO BMI classification system, the US Navy body fat method, and established hydration guidelines from the National Academies of Sciences.

BMI — Body Mass Index Explained

Body Mass Index (BMI) is a screening tool that divides your weight in kilograms by the square of your height in meters (kg/m²). The WHO classifies results as: Underweight (<18.5), Normal weight (18.5–24.9), Overweight (25–29.9), and Obese (≥30). While BMI doesn't directly measure body fat and doesn't account for muscle mass, age, or bone density, it remains the most widely used population-level health screening tool worldwide. Athletes and muscular individuals may have high BMIs despite low body fat, while older adults may have normal BMI with excess fat.

Calories & TDEE — How Many Calories Should You Eat?

Total Daily Energy Expenditure (TDEE) is the total number of calories your body burns in a day, accounting for basal metabolism plus physical activity. It's calculated by multiplying your BMR by an activity factor: 1.2 (sedentary), 1.375 (light activity), 1.55 (moderate), 1.725 (active), or 1.9 (very active). To lose 1 kg per month, create a deficit of approximately 250 calories per day (about 7,700 calories per kg of fat). To gain muscle, add 200–300 calories above TDEE combined with resistance training.

BMR — Basal Metabolic Rate

Your Basal Metabolic Rate is the number of calories your body needs to maintain basic functions at complete rest — breathing, circulation, cell production, and temperature regulation. The Mifflin-St Jeor formula (1990) is considered most accurate for most people: Male BMR = 10W + 6.25H − 5A + 5; Female BMR = 10W + 6.25H − 5A − 161, where W = weight in kg, H = height in cm, A = age in years. BMR typically accounts for 60–70% of total daily calories burned.

Frequently Asked Questions

Is BMI accurate for everyone? ▼

BMI has known limitations. It doesn't distinguish fat from muscle, so athletes may be classified as overweight. It also doesn't account for fat distribution — abdominal fat is more dangerous than fat elsewhere. Different ethnic groups may have different risk thresholds (South Asians, for example, have higher metabolic risk at lower BMIs). Use BMI alongside waist circumference, body fat percentage, and a healthcare provider's assessment.

How many calories do I need to lose weight? ▼

A safe, sustainable rate of weight loss is 0.5–1 kg per week, requiring a daily caloric deficit of 500–1,000 calories. Never consume less than 1,200 calories (women) or 1,500 calories (men) per day without medical supervision. Combining moderate caloric restriction with regular exercise is more effective long-term than diet alone.

What is a healthy body fat percentage? ▼

For men, 6–17% is considered athletic to fitness range, 18–24% is average, and 25%+ is considered obese. For women, 14–24% is athletic to fitness, 25–31% is average, and 32%+ is obese. Women naturally carry more essential fat (10–13%) than men (2–5%) due to hormonal and reproductive functions.

How much water should I drink daily? ▼

The National Academies recommend approximately 3.7L for men and 2.7L for women total daily water intake (from all beverages and food). A simple guideline is 30–35ml per kg of body weight. Your needs increase with physical activity, heat, illness, pregnancy, and breastfeeding. The clearest indicator of adequate hydration is pale yellow urine.