BMI + Calorie Calculator
Mifflin-St Jeor equation — accurate for most adults
Calculate your Body Mass Index and daily calorie target (TDEE) in one place. Based on the Mifflin-St Jeor equation — the most accurate BMR formula for most adults.
Mifflin-St Jeor equation — accurate for most adults
BMI (Body Mass Index) is the most widely used screening tool in clinical medicine for evaluating weight status. Its formula — weight in pounds divided by height in inches squared, multiplied by 703 — produces a single number that correlates with body fat percentage across populations. Like most screening tools, it is useful as a population-level classifier and imperfect as an individual diagnostic.
BMI does not distinguish between muscle and fat mass. A well-trained athlete with 15% body fat and significant muscle may register as overweight or even obese on the BMI scale. An older adult who has lost muscle mass (sarcopenia) may register as normal weight despite elevated metabolic risk. Clinical practitioners typically use BMI as one data point among several — alongside waist circumference, metabolic blood markers, and clinical judgment. The standard categories are: Underweight below 18.5, Normal weight 18.5–24.9, Overweight 25–29.9, Obese 30 and above. These thresholds were established through population studies linking BMI to mortality and disease risk.
This calculator uses the Mifflin-St Jeor equation, preferred by most registered dietitians and the American Dietetic Association for estimating resting metabolic rate. For men: (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5. For women: (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161. This gives your basal metabolic rate — the calories you would burn at complete rest — which is then multiplied by an activity factor to get your Total Daily Energy Expenditure (TDEE).
The activity multiplier is often where estimates go wrong. The categories in this calculator range from sedentary (1.2) to extremely active (1.9). Most desk workers who exercise three times per week land around 1.375–1.55. People tend to overestimate their activity level. If your calculated TDEE is 2,400 and you use 1.55 when 1.375 is more accurate, you are overestimating your calorie budget by roughly 250 calories — enough to produce 26 pounds of weight gain per year if you eat to that number consistently.
A pound of body fat stores approximately 3,500 kilocalories. A consistent daily deficit of 500 calories creates a theoretical one-pound-per-week loss rate. In practice, metabolic adaptation and water weight changes mean actual results vary — the first few weeks typically produce faster loss driven by water weight, followed by slower but more representative fat loss. For most healthy adults, deficits larger than 750 calories per day increase the risk of muscle loss, micronutrient deficiency, and metabolic adaptation. Sustainable loss of 0.5–1 pound per week is more durable than aggressive deficits that trigger compensatory eating and fatigue.