Calculate your Basal Metabolic Rate — the calories your body burns at complete rest, just to stay alive.
Units
Sex
Your BMR
—kcal/day
Basal Metabolic Rate (Mifflin-St Jeor)
Calories burned at complete rest — before any activity
Your TDEE by Activity Level
Sedentary (desk job)—
Lightly active (1–3×/week)—
Moderately active (3–5×/week)—
Very active (6–7×/week)—
Extra active (physical job / 2×/day)—
BMR is calculated using the Mifflin-St Jeor equation — the gold standard for most adults. Multiply by your activity factor to get your TDEE (maintenance calories).
What Is BMR?
Basal Metabolic Rate (BMR) is the minimum number of calories your body needs to perform basic life-sustaining functions — breathing, blood circulation, cell production, nutrient processing, and temperature regulation. Think of it as the energy cost of simply being alive.
Your brain alone consumes roughly 20% of your BMR despite making up only about 2% of your body weight. Your liver, kidneys, and heart account for another large chunk.
Did you know? If you slept for 24 hours straight, you'd still burn your BMR in calories. Your heart beats ~100,000 times a day — that requires fuel.
The Mifflin-St Jeor Equation
This calculator uses the Mifflin-St Jeor equation, published in 1990 and widely regarded as the most accurate BMR formula for the general population. It replaced the older Harris-Benedict equation (1919).
The formulas:
Men: (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) + 5
Women: (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) − 161
Research note: A 2005 review by Frankenfield et al. found Mifflin-St Jeor was accurate within 10% for 82% of people — better than any other predictive equation tested.
Factors That Affect Your BMR
Your BMR isn't fixed — several factors influence how many calories you burn at rest:
Muscle mass: Muscle burns ~6 kcal/lb at rest compared to fat at ~2 kcal/lb. More muscle = higher BMR.
Age: You lose ~3–8% of muscle mass per decade after 30 (a process called sarcopenia), which gradually lowers BMR.
Sex: Men typically have a 5–10% higher BMR than women of similar size due to greater lean mass.
Genetics: Variation of up to 200–300 kcal/day between individuals of similar size and composition (Bouchard, 1990).
Thyroid function: Hypothyroidism can decrease BMR by 5–15%; hyperthyroidism can increase it.
Temperature: Cold exposure activates brown fat and increases BMR — your body burns extra calories to stay warm.
How to Increase Your BMR
While you can't control your age or genetics, there are evidence-based ways to raise your resting metabolism:
Resistance training: Building muscle is the most effective long-term strategy. Muscle tissue is metabolically active even at rest.
Higher protein intake: Protein has a thermic effect of 20–30% (your body burns 20–30% of protein calories just digesting them), compared to 5–10% for carbs and 0–3% for fat.
Avoid crash diets: Extreme calorie restriction (below 1,200 kcal) can lower BMR by 15–20% through metabolic adaptation — your body fights back by burning less.
Did you know? Adding 4.5 kg (10 lbs) of muscle increases your daily burn by ~50 kcal — that's 2.3 kg of fat loss per year without changing your diet.
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