BMR Calculator

BMR (basal metabolic rate) is the estimated calories your body burns at complete rest over 24 hours — the energy needed to maintain basic organ function, breathing, circulation, and temperature regulation. TDEE (total daily energy expenditure) adds all movement, exercise, and thermic effect of food on top of BMR. BMR is the floor; TDEE is what you actually burn day-to-day. Most people's TDEE is 1.2–1.9× their BMR depending on how active they are.

For the general population, Mifflin-St Jeor (1990) is considered the most accurate because it was validated against indirect calorimetry across a broad population. Harris-Benedict (revised 1984) tends to run slightly higher. Katch-McArdle is more accurate specifically for lean individuals who know their body fat percentage, because it calculates lean body mass directly rather than estimating from height and weight alone — which can be misleading for muscular or obese individuals. The spread between formulas gives you a realistic sense of estimate uncertainty.

Sedentary (1.2): desk job, no deliberate exercise. Lightly active (1.375): light exercise 1–3 days per week. Moderately active (1.55): moderate exercise 3–5 days per week — the most common starting point. Very active (1.725): hard training 6–7 days per week. Extra active (1.9): very hard training plus a physically demanding job. Most people overestimate their activity level — if unsure, start with moderately active and track real weight trends for 2–3 weeks before adjusting.

BMR formulas are statistical regression equations fitted to population averages. They cannot account for muscle mass vs fat mass at the same weight, hormonal status (thyroid, cortisol, insulin), sleep quality, chronic illness, medications, and individual metabolic adaptation from dieting history. A person who has been in a long calorie deficit may have a BMR significantly below their formula prediction. Treat BMR as a starting estimate, then calibrate from real-world weight change data over 2–4 weeks.

No. BMR represents calories at complete rest — lying in bed, not moving, not even digesting food. Using BMR as your calorie target would create a deficit large enough to cause muscle loss, fatigue, and metabolic slowdown in most people. Use TDEE (BMR × activity factor) as your maintenance target, then apply a modest deficit (typically 300–500 kcal/day) for weight loss or a surplus for muscle gain. Always aim for a minimum intake above your BMR.

Formula spread is the difference between the highest and lowest BMR estimate across the three formulas. A spread of 80–150 kcal/day is normal. This spread reflects the genuine uncertainty in BMR estimation — not a calculation error. Rather than picking one "correct" number, use the average as your baseline and treat the range as a confidence interval. Your actual metabolic response over 2–4 weeks of consistent tracking is more informative than any formula output.