Health⏱ 5 min read
How Many Calories Do You Burn at Rest? BMR vs TDEE Explained
You burn calories even while sleeping. Understanding the difference between BMR and TDEE — and how to calculate both — is the foundation of any effective nutrition plan.
Basal Metabolic Rate (BMR) is the energy your body needs to sustain vital functions at complete rest. It is not a diet number — it is a biological floor. Total Daily Energy Expenditure (TDEE) is BMR plus everything else you do.
BMR: What It Measures
BMR accounts for: breathing, circulation, cell repair, temperature regulation,
organ function. Everything your body does while you sleep or lie still.
BMR represents approximately 60-70% of total daily calorie expenditure.
The rest: physical activity (15-30%) and digestion/TEF (8-10%).
Mifflin-St Jeor Equation (most accurate for general use):
Men: BMR = 10 x weight(kg) + 6.25 x height(cm) - 5 x age + 5
Women: BMR = 10 x weight(kg) + 6.25 x height(cm) - 5 x age - 161
Example: 35-year-old woman, 65kg, 168cm:
BMR = 10(65) + 6.25(168) - 5(35) - 161
= 650 + 1050 - 175 - 161
= 1,364 kcal/day
This is the minimum calories needed just to stay alive at rest.
Eating below BMR long-term is unsafe and unsustainable.
TDEE: Adding Activity
TDEE = BMR x Activity Multiplier
Activity multipliers:
Sedentary (desk job, no exercise): BMR x 1.2
Lightly active (light exercise 1-3 days/week): BMR x 1.375
Moderately active (moderate exercise 3-5 days/week): BMR x 1.55
Very active (hard exercise 6-7 days/week): BMR x 1.725
Extra active (physical job + training): BMR x 1.9
Example: BMR 1,364, moderately active (3x gym per week):
TDEE = 1,364 x 1.55 = 2,114 kcal/day
This is the maintenance calorie level — eating this keeps weight stable.
Factors That Affect BMR
Muscle mass: the single biggest variable.
Muscle burns approximately 13 kcal/kg/day at rest.
Fat burns approximately 4.5 kcal/kg/day at rest.
Adding 5kg of muscle (over years of training):
Extra resting calories: 5 x 13 = 65 kcal/day = 23,725 kcal/year
This is why resistance training increases long-term metabolic rate.
Thyroid function: major regulator of BMR.
Hypothyroidism can reduce BMR by 30-40%.
Hyperthyroidism can increase BMR by 20-80%.
Age: BMR decreases approximately 1-2% per decade after age 20.
Mostly due to declining muscle mass, not age itself.
Maintaining muscle mass largely preserves metabolic rate with age.
Adaptive Thermogenesis (Why Diets Slow Your Metabolism)
When in a prolonged calorie deficit, the body adapts:
BMR can drop 10-20% below calculated estimates during dieting.
This metabolic adaptation is called adaptive thermogenesis.
It occurs because:
- Reduced body mass (less mass = less energy to maintain)
- Hormonal changes: lower T3 thyroid, lower leptin, lower testosterone
- Reduced NEAT (non-exercise activity thermogenesis)
To minimise metabolic adaptation:
Keep deficit moderate (not more than 25% below TDEE)
Maintain resistance training throughout
Include diet breaks (2 weeks at maintenance) every 8-12 weeks of cutting