Basal Metabolic Rate Calculators

0 calculators tagged with “Basal Metabolic Rate”

Basal metabolic rate (BMR) is the minimum energy expenditure required to maintain essential physiological functions at complete rest — breathing, circulation, maintaining body temperature, and cellular metabolism. It represents approximately 60–70% of total daily energy expenditure (TDEE) in sedentary individuals. BMR is estimated from body weight, height, age, and sex using validated equations. The Mifflin-St Jeor equation (1990) is currently the most accurate for the general population. TDEE = BMR × physical activity level (PAL) factor.

All Calculators

No calculators found for this topic.

Mifflin-St Jeor Equation

Men: BMR = 10W + 6.25H − 5A + 5. Women: BMR = 10W + 6.25H − 5A − 161. W = weight (kg); H = height (cm); A = age (years). Example: 30-year-old woman, 65 kg, 165 cm: BMR = (10×65) + (6.25×165) − (5×30) − 161 = 650 + 1031.25 − 150 − 161 = 1,370 kcal/day.

TDEE (Total Daily Energy Expenditure)

TDEE = BMR × PAL. PAL multipliers: Sedentary (little/no exercise): × 1.2. Light activity (1–3 days/week): × 1.375. Moderate (3–5 days): × 1.55. Very active (6–7 days): × 1.725. Extra active (athlete/physical job): × 1.9.

Factors Affecting BMR

  • Body composition: lean mass has higher metabolic rate than fat; more muscle → higher BMR
  • Age: BMR decreases ~1–2%/decade after age 20 (sarcopenia)
  • Sex: men typically 5–10% higher BMR (more lean mass)
  • Thyroid hormones: hypothyroidism reduces BMR 20–40%; hyperthyroidism increases it
  • Fever: each 0.5°C rise increases BMR ~7%

Glossary

BMR (Basal Metabolic Rate)
Minimum energy to maintain vital functions at complete rest; Mifflin-St Jeor: men = 10W+6.25H−5A+5; women = 10W+6.25H−5A−161; ~60–70% of TDEE in sedentary individuals.
TDEE (Total Daily Energy Expenditure)
BMR × physical activity level (1.2–1.9); total daily energy used; determines caloric needs for weight maintenance; intake < TDEE = weight loss; intake > TDEE = weight gain.
Mifflin-St Jeor Equation
The most accurate BMR prediction formula; uses weight (kg), height (cm), age, and sex; preferred over Harris-Benedict; within ~10% of measured BMR in most individuals.

Frequently Asked Questions

Basal metabolic rate (BMR) is the energy expended at complete rest to maintain vital functions. Mifflin-St Jeor equation (most accurate): Men: BMR = 10W + 6.25H − 5A + 5. Women: BMR = 10W + 6.25H − 5A − 161. W = kg; H = cm; A = years. Example: 40-year-old man, 80 kg, 178 cm: BMR = 800 + 1112.5 − 200 + 5 = 1717.5 kcal/day. This represents the minimum caloric intake needed if lying still for 24 hours.

BMR: energy at complete rest (basal conditions). TDEE (Total Daily Energy Expenditure): total energy spent in a day = BMR + physical activity + thermic effect of food (~10% of intake) + NEAT (non-exercise activity thermogenesis — fidgeting, posture, daily movement). TDEE = BMR × physical activity level (PAL). For a sedentary person: TDEE ≈ BMR × 1.2. For a very active person (6–7 days intense exercise): TDEE ≈ BMR × 1.725. Practical use: caloric intake = TDEE for weight maintenance; intake < TDEE → weight loss; intake > TDEE → weight gain.

Major BMR modifiers: Thyroid hormones: hypothyroidism reduces BMR 20–40% (weight gain, fatigue, cold intolerance); hyperthyroidism increases BMR 20–80% (weight loss, heat intolerance, tachycardia). Fever: each 0.5°C (1°F) rise increases BMR ~7%; serious illness can raise BMR 30–50% → increased caloric needs in ICU patients. Starvation/severe caloric restriction: BMR adapts downward 15–30% (metabolic adaptation) → major barrier to weight loss maintenance. Pregnancy: BMR increases ~15–20% in the third trimester. Menstrual cycle: BMR is ~5–10% higher in the luteal phase (after ovulation) than follicular phase.

Harris-Benedict (1918, revised 1984): the original and long-standard BMR equation: Men: 88.362 + 13.397W + 4.799H − 5.677A. Women: 447.593 + 9.247W + 3.098H − 4.330A. Mifflin-St Jeor (1990): a newer equation developed from a larger, more representative sample. Mifflin-St Jeor is generally more accurate (within ~10% of measured BMR) and is preferred by most nutrition organizations (Academy of Nutrition and Dietetics). Harris-Benedict tends to overestimate BMR by 5–15%, particularly in obese individuals. In practice: both equations are approximations; indirect calorimetry (measuring actual VO₂ and VCO₂) is the most accurate BMR determination and is used for critically ill patients in ICU.