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Basal Metabolic Rate (BMR) Calculator

Determine the baseline caloric energy required to sustain your body's vital physiological organs at rest using the scientifically validated Mifflin-St Jeor, Harris-Benedict, and Katch-McArdle formulas.

Metabolic Baselines & Caloric Energy Expenditure
Accounts for endocrine and baseline lean tissue differences
Years
Ages 15 to 100
%
Enables Katch-McArdle LBM precision
ft
in
lbs
Multiplied by BMR to compute Total Daily Energy Expenditure (TDEE)
Basal Metabolic Rate (Mifflin-St Jeor)
1,788 Calories/day
Maintenance TDEE: 2,771 Calories/day (Moderately Active)
Mifflin-St Jeor (Primary)
1,788 kcal
Harris-Benedict (Revised)
1,849 kcal
Katch-McArdle (LBM)
1,778 kcal
Resting Energy per Hour
74.5 kcal/hr
Energy Output in Joules
7,481 kJ/day
Body Mass Index (BMI)
25.1 kg/m²

Daily Calorie Targets Based on Physical Goals

Derived from your TDEE of 2,771 kcal
Physical Goal Daily Calorie Intake Caloric Deficit / Surplus Expected Weight Rate
Maintain Current Weight 2,771 kcal/day 0 kcal/day 0.0 kg/week (Stable)
Mild Weight Loss 2,521 kcal/day -250 kcal/day -0.25 kg (-0.55 lbs) / week
Standard Weight Loss 2,271 kcal/day -500 kcal/day -0.50 kg (-1.10 lbs) / week
Fast Weight Loss 1,771 kcal/day -1,000 kcal/day -1.00 kg (-2.20 lbs) / week
Mild Muscle Building 3,021 kcal/day +250 kcal/day +0.25 kg (+0.55 lbs) / week
Rapid Mass Gain 3,271 kcal/day +500 kcal/day +0.50 kg (+1.10 lbs) / week

Basal Metabolic Rate (BMR): The Physiology of Human Energy Expenditure

Basal Metabolic Rate (BMR) represents the absolute minimum quantity of caloric energy your body requires to sustain vital physiological functions in a thermoneutral environment while in a post-absorptive, fully rested state. Even when completely motionless, your organs demand substantial energy: the liver and skeletal muscle account for approximately $27\%$ and $18\%$ of resting energy respectively, followed by the brain ($19\%$), kidneys ($10\%$), and heart ($7\%$).

The Scientific Equations: Mifflin-St Jeor vs. Harris-Benedict

Clinical dietetics utilizes mathematical models validated against indirect calorimetry measurements. The primary and most accurate equation for the general adult population is the Mifflin-St Jeor Formula (introduced in 1990), which exhibits a clinical accuracy rate within $\pm 10\%$ of measured resting metabolic rate:

$$\text{BMR}_{\text{male}} = (10 \times m) + (6.25 \times h) - (5 \times a) + 5$$
$$\text{BMR}_{\text{female}} = (10 \times m) + (6.25 \times h) - (5 \times a) - 161$$

Where metric variables are defined as:

  • $m$: Body mass in kilograms ($\text{kg}$). If measuring in pounds, $m = \frac{\text{lbs}}{2.20462}$.
  • $h$: Stature / height in centimeters ($\text{cm}$). If measuring in inches, $h = \text{inches} \times 2.54$.
  • $a$: Chronological age in completed years.

Revised Harris-Benedict Equation (Roza & Shizgal, 1984)

Originally formulated in 1919 and rigorously re-evaluated in 1984, the revised Harris-Benedict model remains widely referenced in medical literature:

$$\text{BMR}_{\text{male}} = 88.362 + (13.397 \times m) + (4.799 \times h) - (5.677 \times a)$$
$$\text{BMR}_{\text{female}} = 447.593 + (9.247 \times m) + (3.098 \times h) - (4.330 \times a)$$

Katch-McArdle Equation: Accounting for Lean Body Mass (LBM)

For athletes, bodybuilders, or individuals with known body fat percentages, the Katch-McArdle Formula provides superior precision by computing metabolic demand directly from metabolically active lean tissue $L$ rather than total gross body weight:

$$L = m \times \left(1 - \frac{\%BF}{100}\right), \quad \text{BMR} = 370 + (21.6 \times L)$$

From BMR to Total Daily Energy Expenditure (TDEE)

BMR accounts for approximately $60\%$ to $75\%$ of an average person's daily energy output. To determine your total daily calorie requirement, your BMR is multiplied by a Physical Activity Level (PAL) coefficient:

$$\text{TDEE} = \text{BMR} \times \text{Activity Factor}$$
Activity Category Multiplier Lifestyle Description
Sedentary 1.200 Desk job, minimal or no deliberate physical exercise
Lightly Active 1.375 Light exercise or sports 1 to 3 days per week
Moderately Active 1.550 Moderate exercise or intense physical training 3 to 5 days per week
Very Active 1.725 Hard exercise or physical labor 6 to 7 days per week
Extremely Active 1.900 Heavy daily training, endurance athletics, or double workout sessions

Step-by-Step Practical Calculation Example

Consider a 32-year-old male weighing 82 kg (180.8 lbs) with a height of 180 cm (5 ft 11 in) who exercises moderately 4 days per week:

  1. Mifflin-St Jeor BMR: $$\text{BMR} = (10 \times 82) + (6.25 \times 180) - (5 \times 32) + 5 = 820 + 1125 - 160 + 5 = \mathbf{1{,}790 \text{ kcal/day}}$$
  2. Harris-Benedict BMR: $$\text{BMR} = 88.362 + (13.397 \times 82) + (4.799 \times 180) - (5.677 \times 32) = 88.362 + 1098.55 + 863.82 - 181.66 = \mathbf{1{,}869 \text{ kcal/day}}$$
  3. TDEE Calculation (Moderately Active = 1.55): $$\text{TDEE} = 1{,}790 \times 1.55 = \mathbf{2{,}775 \text{ kcal/day}}$$
  4. Target for Safe Fat Loss (0.5 kg / 1.1 lb per week): $$\text{Daily Target} = 2{,}775 - 500 = \mathbf{2{,}275 \text{ kcal/day}}$$
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