Calorie Calculator (TDEE)

BMR vs. TDEE — what's the difference?

Your Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest to maintain basic functions: breathing, circulation, cell production, and temperature regulation. It represents roughly 60–70% of your total daily calorie burn. Your Total Daily Energy Expenditure (TDEE) is your BMR multiplied by an activity factor that accounts for movement, exercise, and the thermic effect of food. TDEE is the number that actually matters for weight management — eat above it and you gain weight, eat below it and you lose weight.

The Mifflin-St Jeor formula

This calculator uses the Mifflin-St Jeor equation, published in 1990 and validated as the most accurate BMR estimator for most adults in a widely cited 2005 comparison study. The formula: for men, BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5. For women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161. The older Harris-Benedict formula (1919) overestimates BMR by 5% on average, which is why this calculator uses Mifflin-St Jeor instead.

TDEE = BMR × activity multiplier. Sedentary (desk job, little exercise): 1.2. Lightly active (light exercise 1–3 days/week): 1.375. Moderately active (moderate exercise 3–5 days/week): 1.55. Very active (hard exercise 6–7 days/week): 1.725. Extra active (physical job + hard training): 1.9. Most people overestimate their activity level — when in doubt, select one tier lower than you think.

Setting calorie targets by goal

For weight loss: subtract 500 calories/day from TDEE for approximately 1 lb/week of fat loss. A 250-calorie deficit targets 0.5 lb/week — slower but easier to sustain with less muscle loss and hunger. Avoid going below 1,200 calories/day for women or 1,500 for men without medical supervision, as very low calorie diets increase muscle loss and nutrient deficiency risk.

For weight gain (muscle building): add 200–300 calories above TDEE ("lean bulk") to maximize muscle gain while minimizing fat gain. Larger surpluses add mostly fat, not muscle — muscle protein synthesis has a ceiling of roughly 0.25–0.5 lbs of muscle per week for natural lifters. For weight maintenance: eat at TDEE.

Why estimates have ~10% error

All BMR formulas are population-level estimates. Individual BMR can vary by ±10% from any formula's prediction due to differences in non-exercise activity thermogenesis (NEAT — fidgeting, posture, unconscious movement), hormone levels (thyroid function significantly affects metabolic rate), gut microbiome composition, and body composition (muscle burns more calories at rest than fat). Treat the calculator's output as a starting point. Track your actual intake and weight for 2–3 weeks, then adjust by 100–200 calories if results diverge from expectations.

Adaptive thermogenesis

The body actively resists both weight loss and weight gain by adjusting metabolic rate — a process called adaptive thermogenesis. In a calorie deficit, TDEE decreases beyond what body weight loss alone would predict, often by 100–300 calories. This "metabolic adaptation" is why weight loss slows after 4–8 weeks even on the same deficit. Recalculate your TDEE every 10–15 lbs of weight lost and update your calorie target accordingly.