BMR Calculator
Your basal metabolic rate is what you would burn in a day if you stayed in bed without moving — the energy cost of keeping the heart, lungs, brain and organs running. Enter age, sex, height and weight and the calculator uses the Mifflin-St Jeor equation (more accurate than the old Harris-Benedict for modern populations) to estimate daily BMR in calories. Multiply by an activity factor and you get TDEE, the figure diets actually care about.
How BMR is estimated
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1
Enter age, sex, height and weight
Metric or imperial. Biological sex is used because male and female bodies differ in lean mass proportion.
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Mifflin-St Jeor equation runs
For men: BMR = 10·kg + 6.25·cm − 5·age + 5. For women: BMR = 10·kg + 6.25·cm − 5·age − 161.
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Adjust with activity factor (optional)
Choose sedentary (×1.2) through very active (×1.9) to estimate total daily energy expenditure.
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4
Read BMR and TDEE
BMR is your at-rest burn. TDEE adds movement. Diets target TDEE minus a deficit for weight loss, TDEE plus a surplus for gain.
Mifflin-St Jeor (1990) — the modern standard
- 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
This equation replaced Harris-Benedict (1919) as the clinical default because it fits contemporary populations within ±10% across a wider range of body types.
Activity factors (Katch-McArdle style)
| Lifestyle | Multiplier |
|---|---|
| Sedentary (desk job, no exercise) | 1.20 |
| Lightly active (1-3 workouts/week) | 1.375 |
| Moderately active (3-5 workouts/week) | 1.55 |
| Very active (6-7 workouts/week) | 1.725 |
| Extremely active (physical job + daily training) | 1.90 |
Example
A 35-year-old woman, 165 cm, 68 kg, moderately active:
- BMR = (10 × 68) + (6.25 × 165) − (5 × 35) − 161
- BMR = 680 + 1031.25 − 175 − 161 ≈ 1,375 kcal/day
- TDEE at 1.55 = 2,131 kcal/day
To lose about 0.5 kg per week, target 2,131 − 500 = 1,631 kcal/day.
Limitations
- Body composition matters: Mifflin assumes average lean mass. Very lean or very muscular people can be off by 200+ kcal.
- Adaptation: after weeks of deficit, metabolism slows (adaptive thermogenesis). Recalculate every few kilos lost.
- Medical conditions (thyroid, medication, illness) shift BMR independently of the equation.
Frequently Asked Questions
Mifflin-St Jeor is the current default in clinical settings because it fits modern body types more closely. Harris-Benedict tends to overestimate by 5-10% on average.
Fitness trackers combine a BMR estimate with step counts and heart rate, and many use Katch-McArdle (which needs body fat percentage). Differences of ±15% are normal across methods.
It drops roughly 1-2% per decade after 20, mostly due to loss of lean mass. Resistance training slows this decline significantly.
Close but not identical. BMR is measured after a full night’s sleep, 12 hours fasted, in a neutral environment. RMR is measured under looser conditions and usually lands about 10% higher.