BMR Calculator

Your Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest — the energy required just to keep your heart beating, lungs breathing, body temperature regulated, and brain functioning. BMR accounts for roughly 60–70% of your total daily calorie burn.

Your Total Daily Energy Expenditure (TDEE) takes BMR and multiplies it by an activity factor to account for all the movement in your day: walking, exercise, work, even fidgeting. TDEE is the number you use for weight management decisions — eating at TDEE maintains weight, eating below it causes weight loss, eating above it causes weight gain.

This calculator uses the Mifflin-St Jeor equation, published in 1990 and consistently shown to be the most accurate BMR formula for most adults. Studies show it's accurate within 10% for roughly 80% of non-obese, non-athletic individuals. The older Harris-Benedict equation is commonly cited but systematically overestimates by 5–15%.

The activity multipliers deserve careful reflection. Most people significantly overestimate their activity level. "Sedentary" means a desk job with minimal intentional exercise. "Lightly active" applies to 1–3 days of light exercise per week. "Moderately active" means 3–5 days of moderate exercise. "Very active" means 6–7 days of hard exercise. "Extremely active" applies to physical laborers or twice-daily training — this is genuinely rare.

For weight loss: subtract 500 calories from TDEE for approximately 1 pound per week loss (a 3,500-calorie deficit = 1 lb of fat). Never go below 1,200 calories per day for women or 1,500 for men without medical supervision — very low intakes cause muscle loss, hormonal disruption, and metabolic adaptation.

Recalculate your TDEE every 10–15 pounds of weight change, or every time your activity level changes significantly.