BMR Calculator
Calculate your Basal Metabolic Rate — the calories your body burns at complete rest.
What Is Basal Metabolic Rate?
Your Basal Metabolic Rate (BMR) is the energy your body burns at complete rest — the cost of breathing, circulating blood, regulating temperature, repairing cells and keeping your brain running. For most people BMR is the single largest component of daily calorie burn, typically 60–70% of the total. Even a completely sedentary day costs well over a thousand calories.
The Two Formulas This Calculator Uses
Mifflin-St Jeor (1990) — the modern standard, recommended by the Academy of Nutrition and Dietetics:
- Men: (10 × weight kg) + (6.25 × height cm) − (5 × age) + 5
- Women: (10 × weight kg) + (6.25 × height cm) − (5 × age) − 161
Harris-Benedict (revised 1984) — the classic formula, shown for comparison:
- Men: 88.362 + (13.397 × weight kg) + (4.799 × height cm) − (5.677 × age)
- Women: 447.593 + (9.247 × weight kg) + (3.098 × height cm) − (4.330 × age)
The two usually land within 5% of each other. Mifflin-St Jeor tends to be more accurate for modern populations, which is why we use it as the primary result.
Worked Example
A 28-year-old woman, 62 kg, 168 cm: BMR = (10 × 62) + (6.25 × 168) − (5 × 28) − 161 = 620 + 1,050 − 140 − 161 = 1,369 kcal/day. That's what her body burns before any movement at all.
What Raises or Lowers Your BMR
| Factor | Effect on BMR |
|---|---|
| More muscle mass | Raises it — muscle burns ≈13 kcal/kg/day at rest vs ≈4.5 for fat |
| Ageing | Lowers it ≈1–2% per decade after 20, mostly via muscle loss |
| Prolonged severe dieting | Lowers it (adaptive thermogenesis) |
| Thyroid hormones | Hyperthyroidism raises, hypothyroidism lowers |
| Body size | Bigger bodies burn more in absolute terms |
BMR vs RMR — Is There a Difference?
Strictly, yes. BMR is measured under laboratory conditions after an overnight fast and full rest; Resting Metabolic Rate (RMR) is measured under looser conditions and runs about 10% higher. Calculators like this one estimate something between the two, which is fine for everyday planning.
How To Use Your BMR Number
Never eat at or below your BMR for fat loss — that's a common and counterproductive mistake. Instead, multiply your BMR by an activity factor (1.2 for sedentary up to 1.9 for extremely active) to get your true daily burn, or simply use our calorie calculator, which does it for you and adds goal-based targets. To preserve the muscle that keeps your BMR high while dieting, check our protein calculator.
Frequently Asked Questions
Can I speed up my metabolism?
Meaningfully, in two ways: build muscle (each kilogram adds roughly 13 kcal/day at rest, plus much more through training itself), and avoid prolonged extreme deficits that trigger metabolic adaptation. Green tea, cold showers and 'metabolism-boosting' foods have effects too small to matter.
Is it dangerous to eat below my BMR?
Eating below BMR isn't automatically dangerous for short periods, but it usually signals an overly aggressive deficit. It makes adequate protein and micronutrient intake very difficult and accelerates muscle loss. Set targets from TDEE, not BMR.
Why is my BMR lower than my friend's?
BMR scales mainly with body size and lean mass. Someone taller, heavier or more muscular burns more at rest. Age and sex matter too — the formulas subtract calories for each year of age, and women's BMR averages lower due to body composition.
How accurate are BMR formulas?
Mifflin-St Jeor lands within about 10% of laboratory-measured values for most people. Outliers exist — very muscular, very lean or very obese individuals deviate more. Indirect calorimetry at a clinic is the only way to know precisely.