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What is BMR and How is It Calculated? (Mifflin–St Jeor vs Harris–Benedict)

Understand Basal Metabolic Rate — the calories you burn just by existing. Learn both major equations, what factors affect BMR, and how to use it for weight management.

OurDailyCalc Team 5 min read

Your body burns calories even when you’re doing absolutely nothing — sleeping, breathing, maintaining body temperature. That baseline burn is your BMR (Basal Metabolic Rate), and it typically accounts for 60–75% of your total daily calorie expenditure.

The two main equations

Mifflin–St Jeor (1990) — more accurate for modern populations

Male:   BMR = 10×weight(kg) + 6.25×height(cm) − 5×age + 5
Female: BMR = 10×weight(kg) + 6.25×height(cm) − 5×age − 161

Harris–Benedict (revised 1984) — older, still widely used

Male:   BMR = 88.362 + 13.397×weight + 4.799×height − 5.677×age
Female: BMR = 447.593 + 9.247×weight + 3.098×height − 4.330×age

The American Dietetic Association recommends Mifflin–St Jeor as the most reliable for healthy adults.

What affects BMR?

  1. Muscle mass — Muscle burns more calories at rest than fat
  2. Age — BMR decreases ~2% per decade after 20
  3. Gender — Men typically have higher BMR (more muscle mass)
  4. Body size — Larger bodies need more energy to maintain
  5. Genetics — Some people genuinely have faster metabolisms
  6. Thyroid function — Hypothyroidism can lower BMR significantly

BMR vs TDEE

BMR is rest-only. Your actual daily burn (TDEE) adds physical activity:

TDEE = BMR × Activity Multiplier

Sedentary:       ×1.2
Lightly active:  ×1.375
Moderately active: ×1.55
Very active:     ×1.725
Extremely active: ×1.9

How to use BMR for weight management

  • Weight loss: Eat below TDEE but never below BMR
  • Weight gain: Eat 300–500 above TDEE consistently
  • Maintenance: Eat at TDEE

Eating below BMR signals “starvation” to your body — it slows metabolism, breaks down muscle, and triggers intense hunger. This is why crash diets fail.

Worked example

Female, 30 years old, 62 kg, 165 cm:

Mifflin: 10(62) + 6.25(165) − 5(30) − 161 = 620 + 1031 − 150 − 161 = 1,340 cal
TDEE (lightly active): 1,340 × 1.375 = 1,843 cal
Weight loss target: 1,843 − 400 = ~1,443 cal/day

Calculate yours with the OurDailyCalc BMR calculator — it shows both equations plus TDEE for all activity levels.

TL;DR

  • BMR = calories burned at complete rest (60–75% of daily burn)
  • Mifflin–St Jeor is the most accurate modern equation
  • Never eat below your BMR — it damages metabolism
  • TDEE = BMR × activity level — this is what actually matters for weight goals
#bmr #metabolism #calories #health #nutrition
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OurDailyCalc Team

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