Calculate how many calories your body burns at rest
Your Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest — just to keep you alive. It accounts for breathing, circulation, cell production, protein synthesis, and all other basic physiological functions. BMR typically represents 60–75% of your total daily calorie expenditure.
This calculator uses the Mifflin-St Jeor equation, which is considered the most accurate BMR formula for most people according to the Academy of Nutrition and Dietetics:
Men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5
Women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161
A 35-year-old woman weighing 65 kg and 168 cm tall: BMR = (10 × 65) + (6.25 × 168) − (5 × 35) − 161 = 650 + 1,050 − 175 − 161 = 1,364 calories per day.
BMR is your resting baseline. Multiply by an activity factor to get your Total Daily Energy Expenditure (TDEE) — the calories you actually need each day:
| Activity level | Description | Multiplier |
|---|---|---|
| Sedentary | Desk job, little or no exercise | BMR × 1.2 |
| Lightly active | Light exercise 1–3 days/week | BMR × 1.375 |
| Moderately active | Moderate exercise 3–5 days/week | BMR × 1.55 |
| Very active | Hard exercise 6–7 days/week | BMR × 1.725 |
| Extremely active | Physical job + daily training | BMR × 1.9 |
BMR naturally decreases with age — approximately 1–2% per decade after age 20. This is partly due to loss of muscle mass (sarcopenia), which is metabolically more active than fat tissue. A 50-year-old typically has a BMR 10–15% lower than they did at 25, assuming no change in body composition.
This is why maintaining or building muscle through resistance training becomes increasingly important with age — it directly supports a higher BMR and makes it easier to maintain a healthy weight without dramatically cutting calories.
Beyond age and sex, several factors influence BMR. Muscle mass is the biggest variable — each kilogram of muscle burns approximately 13 calories per day at rest versus 4.5 calories for fat. Thyroid function significantly affects metabolic rate — hypothyroidism can reduce BMR by 30–40%. Body temperature, fever, and illness temporarily raise BMR. Extreme caloric restriction reduces BMR as the body adapts to conserve energy — one reason very low-calorie diets often plateau.
BMR is the calories burned at complete rest. TDEE (Total Daily Energy Expenditure) adds the calories burned through physical activity and the thermic effect of food. TDEE is the number you should actually use for nutrition planning — BMR alone underestimates your needs.
The Mifflin-St Jeor equation is accurate within ±10% for most people. It is less accurate for very muscular individuals (underestimates BMR) and people with very high body fat (overestimates BMR). The only truly accurate BMR measurement requires indirect calorimetry in a clinical setting.
No — eating at BMR would put you in a severe calorie deficit unless you are completely sedentary. Use your TDEE (BMR × activity factor) as the baseline, then adjust based on your goal: eat below TDEE to lose weight, at TDEE to maintain, or above TDEE to gain muscle.
Yes — the most effective way is to build muscle mass through resistance training. Muscle is metabolically expensive tissue that burns calories continuously. Other factors: eating adequate protein (the thermic effect of protein is higher than carbs or fat), staying hydrated, and getting sufficient sleep (sleep deprivation reduces metabolic rate).
Men typically have more muscle mass and less body fat than women of the same weight and height. Since muscle burns more calories than fat, men have higher BMRs. Hormonal differences also play a role — testosterone supports muscle retention and a slightly higher metabolic rate.