Calorie Calculator (BMR & TDEE, Mifflin-St Jeor)
Enter age, sex, height, weight, and activity level to estimate your basal metabolic rate (BMR), total daily energy expenditure (TDEE), and calorie targets for weight loss, maintenance, or gain.
How it works
How the calculator works
BMR (basal metabolic rate) is the calories your body burns at rest just to keep you alive — running your heart, brain, kidneys, and so on. We compute it with the Mifflin-St Jeor equation, which has been validated against indirect calorimetry as the most accurate of the simple BMR formulas: BMR = 10×kg + 6.25×cm − 5×age + 5 (men) or − 161 (women).
TDEE (total daily energy expenditure) is BMR × an activity multiplier (1.2 for sedentary up to 1.9 for athletes). To lose about 0.45 kg / 1 lb per week, eat about 500 kcal/day below TDEE; to gain it, eat 500 above. The mild numbers (±250) target half-pound weekly change.
Why this is an estimate, not a measurement
Mifflin-St Jeor has a published standard error of about 10%. Two people with the same age, sex, height, and weight can have BMRs that differ by 200-300 kcal due to body composition (more muscle = higher BMR), genetics, and adaptive metabolism after weight changes.
Treat the TDEE number as a starting estimate, not a target. Track your weight weekly: if it doesn't change after two weeks at the calculated maintenance level, your true TDEE is probably 100-200 kcal off in one direction. Adjust intake based on observed change, not on the calculator alone.
Common pitfalls
Activity multiplier inflation. Most people overestimate their activity. 'Moderate' (1.55) means three to five real workouts a week — not 'I walk to the office'. Picking too high a multiplier inflates the calorie target and explains why many calorie-tracked diets stall.
Logging accuracy. Studies show people under-report calorie intake by 20-30% even when actively tracking. If your weight isn't moving as predicted, check portion measurements and untracked drinks before adjusting the calculator inputs.
Adaptive metabolism. Sustained calorie deficits lower BMR by 5-15% over weeks (the body 'turns down the thermostat'). Recompute every 4-6 kg of weight change.
Frequently asked questions
›Which formula is used?
Mifflin-St Jeor (1990), the most accurate of the common BMR equations. Harris-Benedict (older) overestimates by ~5%; the Katch-McArdle formula uses lean body mass and is more accurate if you know yours.
›Why does sex change the result?
Average body composition differs — men typically have more lean mass at the same weight, which raises BMR. The formula accounts for this with a +5 / −161 offset.
›Is this accurate for athletes?
Less so. Mifflin-St Jeor was validated on the general population. Athletes with high muscle mass should consider the Katch-McArdle formula or in-lab indirect calorimetry.
›What's the difference between BMR and TDEE?
BMR is at-rest calories. TDEE is BMR plus calories from movement, digestion, and exercise. TDEE = BMR × activity factor.
›How fast should I lose weight?
Most evidence-based guidelines suggest 0.5-1% of body weight per week. For a 75 kg person that's 0.4-0.75 kg/week, which the −250 to −500 targets cover.
›Should I subtract more than 500 kcal?
Larger deficits accelerate loss but also accelerate muscle loss and metabolic adaptation. Most professionals cap deficits at about 25% below TDEE.
›What about macronutrients?
This calculator gives total calories. A common starting macro split: protein 1.6-2.2 g/kg of bodyweight, fat 0.8-1.0 g/kg, carbs to fill the remaining calories.
›Does the data leave my browser?
No. Calculation runs locally; nothing is sent to a server.
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