Basal Metabolic Rate (BMR) represents the absolute minimum quantity of energy, measured in kilocalories per day, required to maintain standard metabolic homeostasis and sustain life-support systems (such as cell division, neural signaling, cardiovascular function, and cellular respiration) while at complete physical and digestive rest in a thermoneutral environment. Historically evaluated in clinical settings using indirect calorimetry, BMR is estimated in modern nutrition and healthcare using mathematical equations that model metabolic rate based on gender, body weight, height, and age. The two most prominent estimation models are the Mifflin-St Jeor equation (formulated in 1990 and favored for modern lifestyles) and the Revised Harris-Benedict equation (derived in 1919 and updated in 1984 by Roza and Shizgal). Additionally, the Katch-McArdle formula calibrates BMR using lean body mass, making it highly accurate for athletic populations. BMR serves as the metabolic foundation from which Total Daily Energy Expenditure (TDEE) is derived by applying activity-level multipliers. Identifying an accurate BMR is critical for establishing structured meal plans, predicting weight trajectory, and tailoring sports nutrition protocols.
Mathematical Formula & Logic
BMR calculations are performed using three distinct mathematical models, stratified by biological sex or body composition:
1. Mifflin-St Jeor Equation:
- Men: BMR = (10 × Weight_kg) + (6.25 × Height_cm) - (5 × Age_years) + 5
- Women: BMR = (10 × Weight_kg) + (6.25 × Height_cm) - (5 × Age_years) - 161
2. Revised Harris-Benedict Equation (1984):
- Men: BMR = 88.362 + 13.397 × Weight_kg + 4.799 × Height_cm - 5.677 × Age_years
- Women: BMR = 447.593 + 9.247 × Weight_kg + 3.098 × Height_cm - 4.330 × Age_years
3. Katch-McArdle Formula (LBM Based):
- BMR = 370 + 21.6 × LBM
- LBM = Weight_kg × (1 - Body_Fat_Percentage / 100)
Where:
- Weight_kg = Body mass in kilograms
- Height_cm = Height in centimeters
- Age_years = Age in years
- LBM = Lean Body Mass in kilograms
Step-by-Step Example
Estimate the BMR for a 25-year-old male who is 175 cm tall and weighs 70 kg (assuming 20% body fat) using all three formulas:
1. Mifflin-St Jeor calculation:
BMR = (10 × 70) + (6.25 × 175) - (5 × 25) + 5 = 1,673.75 kcal/day
2. Revised Harris-Benedict calculation:
BMR = 88.362 + (13.397 × 70) + (4.799 × 175) - (5.677 × 25) = 1,724.052 kcal/day
3. Katch-McArdle calculation:
LBM = 70 × (1 - 20 / 100) = 56 kg
BMR = 370 + (21.6 × 56) = 1,579.6 kcal/day
4. The Mifflin-St Jeor model estimates BMR at 1,674 kcal/day, the Revised Harris-Benedict model estimates BMR at 1,724 kcal/day, and the Katch-McArdle model estimates BMR at 1,580 kcal/day.
Reference Data & Values
gender
weight
height
age
bmr mifflin
bmr harris
bmr katch
Male
70 kg
175 cm
25
1,674 kcal
1,724 kcal
1,580 kcal (20% BF)
Female
70 kg
175 cm
25
1,508 kcal
1,533 kcal
1,459 kcal (28% BF)
Male
90 kg
185 cm
35
1,886 kcal
1,982 kcal
1,925 kcal (20% BF)
Female
60 kg
165 cm
35
1,300 kcal
1,348 kcal
1,303 kcal (28% BF)
Frequently Asked Questions
Basal Metabolic Rate (BMR) is the amount of energy (in calories) your body needs to stay alive and function at rest, without any physical activity. It powers basic life-support systems like your brain, heart, lungs, and kidneys.
For most adults, the Mifflin-St Jeor formula is considered the most accurate estimation equation. However, if you know your exact body fat percentage, the Katch-McArdle formula is superior because it uses lean body mass.
As you age, your BMR typically decreases. This decline is primary due to a gradual loss of muscle mass (sarcopenia) and an increase in fat mass as you grow older.
BMR is the energy burned for survival at complete rest. TDEE (Total Daily Energy Expenditure) is BMR plus the calories burned through activity (exercise, walking, working) and digestion.
Yes, muscle tissue is more metabolically active than fat tissue. Every pound of muscle burns about 6 calories per day at rest, compared to 2 calories burned by a pound of fat.
To lose weight, you should eat fewer calories than your TDEE, but generally not fewer calories than your BMR. Eating below your BMR can trigger metabolic adaptation (slowdown) and lethargy.
Men generally have higher BMRs than women of the same weight and height because men typically have a percentage of lean muscle mass and less body fat.
Standard BMR equations like Mifflin-St Jeor are not validated for pregnant women. Pregnancy increases metabolic demand dynamically, requiring clinical guidelines rather than general formulas.