Your Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest — just to keep you alive. Breathing, heartbeat, brain activity, cell repair — all of this costs energy.
BMR accounts for roughly 60–75% of your total daily calorie burn. Knowing it is the first step to calculating your TDEE.
What Is BMR?
BMR measures the calories your body needs for 24 hours of complete rest — fasting, at a neutral temperature. It depends on:
- Body weight — more mass requires more energy
- Height — larger body surface area needs more energy
- Age — BMR decreases with age
- Gender — men have a higher BMR on average
- Muscle mass — muscle burns more energy than fat
The Mifflin-St Jeor Formula
The Mifflin-St Jeor formula (1990) is considered the most accurate method for calculating BMR. It is recommended by the Academy of Nutrition and Dietetics:
Men: BMR = 10 × Weight(kg) + 6.25 × Height(cm) − 5 × Age + 5
Women: BMR = 10 × Weight(kg) + 6.25 × Height(cm) − 5 × Age − 161
Example: A 30-year-old male, 180 cm, 80 kg: 10 × 80 + 6.25 × 180 − 5 × 30 + 5 = 1,780 kcal/day.
The Harris-Benedict Formula
The Harris-Benedict formula was developed in 1919 and revised by Roza & Shizgal in 1984. It tends to produce slightly higher values than Mifflin-St Jeor:
Men: BMR = 13.397 × Weight(kg) + 4.799 × Height(cm) − 5.677 × Age + 88.362
Women: BMR = 9.247 × Weight(kg) + 3.098 × Height(cm) − 4.330 × Age + 447.593
Harris-Benedict tends to slightly overestimate BMR — especially in overweight individuals. For most people, Mifflin-St Jeor is the better choice.
From BMR to Total Daily Burn
Your BMR is only part of the picture. To find your actual daily calorie needs, multiply BMR by an activity factor:
| Activity Level | Factor | Example (BMR 1,780) |
|---|---|---|
| Sedentary | 1.2 | 2,136 kcal |
| Lightly active | 1.375 | 2,448 kcal |
| Moderately active | 1.55 | 2,759 kcal |
| Very active | 1.725 | 3,070 kcal |
| Extremely active | 1.9 | 3,382 kcal |
The result is your TDEE (Total Daily Energy Expenditure) — the foundation of any nutrition plan. Learn more in our TDEE guide.
Calculate your BMR now
Mifflin-St Jeor and Harris-Benedict compared — free and no sign-up required.
Calculate for free now →What Affects Your BMR?
Beyond the standard factors (weight, height, age, gender), several other things influence your BMR:
- Muscle mass: Muscle burns significantly more calories at rest than fat tissue. Strength training can permanently increase your BMR.
- Thyroid function: Thyroid hormones regulate metabolism. An underactive or overactive thyroid directly affects BMR.
- Crash diets: Extreme calorie restriction lowers BMR — your body adapts and burns less (metabolic adaptation).
- Genetics: Individual genetic differences can cause BMR to vary by 5–10%.
BMR and Nutrition Goals
Your BMR is the absolute floor of your calorie intake. You should never consistently eat below your BMR. For healthy weight loss, aim for a moderate calorie deficit of 300–500 kcal below your TDEE.
How to split your calories optimally is covered in our macronutrient guide.
Conclusion
BMR is the foundation of every nutrition calculation. Calculate your BMR with our calculator and use the result to determine your total daily energy expenditure.
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