BMR vs TDEE Calculator: How to Calculate Both

The Mifflin-St Jeor Equation: The Gold Standard for BMR

Published in 1990 and validated against indirect calorimetry measurements in over 500 subjects, the Mifflin-St Jeor equation is the most accurate widely-available BMR prediction formula and is recommended by the Academy of Nutrition and Dietetics, the American Dietetic Association, and the International Society of Sports Nutrition. For men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) + 5. For women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) − 161. For example, a 35-year-old woman weighing 65 kg and standing 165 cm tall calculates to BMR = (10 × 65) + (6.25 × 165) − (5 × 35) − 161 = 650 + 1031.25 − 175 − 161 = 1,345 kcal/day. The equation is typically accurate within ±10% of measured resting metabolic rate.

How to Convert BMR to TDEE

Once you have your BMR, multiplying it by an activity factor produces your TDEE. The conversion is straightforward: TDEE = BMR × Activity Factor. Using the same 35-year-old woman with a BMR of 1,345 kcal: if she is sedentary (1.2), TDEE = 1,614 kcal; lightly active (1.375), TDEE = 1,849 kcal; moderately active (1.55), TDEE = 2,085 kcal; very active (1.725), TDEE = 2,320 kcal; extra active (1.9), TDEE = 2,556 kcal. That single activity choice swings the estimate by nearly 940 kcal/day — which is why selecting the right multiplier is the most consequential step in the entire calculation.

Detailed Activity Factor Guide

Select the multiplier that best matches your average daily reality, not your goal or your best day. Sedentary (1.2): desk job, no regular exercise, minimal daily walking. Lightly Active (1.375): desk job plus 1-3 days/week of light activity such as casual walking, yoga, or light gym sessions of 30 minutes. Moderately Active (1.55): desk or light job plus 3-5 days/week of moderate exercise such as jogging, cycling, or resistance training sessions of 45-60 minutes. Very Active (1.725): physically active job or 6-7 days/week of vigorous training. Extra Active (1.9): elite athletes, construction workers, or anyone who trains twice daily with high intensity.

Common Calculation Errors and How to Avoid Them

Overestimating activity is the most common error, responsible for 40-60% of failed diet attempts according to dietary adherence research. People consistently rate themselves as "moderately active" or "very active" when their objective step counts and training volume match a sedentary or lightly active profile. A desk job with 2-3 gym sessions per week is genuinely "lightly active" (1.375), not "moderately active" (1.55), because exercise only occupies 1-2 hours of a 24-hour day. The second most common error is using pounds and inches instead of kg and cm in the Mifflin-St Jeor equation, which produces dramatically wrong results — always convert: 1 lb = 0.454 kg, 1 inch = 2.54 cm.

Practical Use: Setting Your Calorie Target

For weight maintenance, eat at your calculated TDEE. For fat loss, subtract 500-750 kcal from your TDEE. For muscle gain, add 250-500 kcal to your TDEE. After 2-3 weeks of consistent eating at your target, compare your actual body weight change to the predicted change. If you are losing faster than 0.75 kg/week during a cut, increase intake by 100-200 kcal. If you are gaining weight during a cut, decrease intake by the same amount. This feedback loop turns the calculator from a static formula into a dynamic tool that refines your personal TDEE over time. Expect your real TDEE to differ from the formula by 10-15% initially, narrowing to within 5% after two refinement cycles.