Basal Metabolic Rate (BMR) Calculator

The Formula

BMRThe number of calories your body needs at complete rest to maintain vital functions like breathing, circulation, and cell production. is the number of calories your body burns at complete rest to sustain basic physiological functions. It is the floor of your caloric needs — you should never eat below this number.

Variable Definitions

How to Use This Calculator

1. 1

   Select your unit system (Imperial or Metric).

2. 2

   Select the BMR formula — Mifflin-St Jeor is recommended for most people.

3. 3

   Enter your sex, age, weight, and height.

4. 4

   Optionally enter body fat % for Katch-McArdle or cross-formula comparison.

5. 5

   The formula line shows the exact math so you can verify the calculation.

Common Applications

• Weight management planning — use BMRThe number of calories your body needs at complete rest to maintain vital functions like breathing, circulation, and cell production. as the baseline for calculating TDEETotal calories burned per day, including BMR plus physical activity and the thermic effect of food. Used for weight management. and setting calorie targets for weight loss, gain, or maintenance with an appropriate deficit or surplus
• Nutrition program design — bodybuilders, athletes, and dietitians use BMRThe number of calories your body needs at complete rest to maintain vital functions like breathing, circulation, and cell production. to establish the minimum safe caloric intake before adding activity and thermic effect adjustments
• Metabolic health assessment — compare BMRThe number of calories your body needs at complete rest to maintain vital functions like breathing, circulation, and cell production. formula results to identify metabolic adaptations from prolonged dieting or to assess how body composition changes affect resting energy expenditure
• Clinical nutrition — healthcare providers use BMRThe number of calories your body needs at complete rest to maintain vital functions like breathing, circulation, and cell production. equations for parenteral nutrition dosing, metabolic monitoring, and estimating energy needs in hospitalized patients

Basal Metabolic Rate (BMR) accounts for 60-75% of total daily calorie burn, far more than physical activity

Understanding the Concept

BMRThe number of calories your body needs at complete rest to maintain vital functions like breathing, circulation, and cell production. is your body's idle fuel consumption — the calories burned for breathing, circulation, cell repair, and temperature regulation while completely at rest. It represents the minimum caloric intake necessary to survive. The safe minimum calorie intake shown is your BMRThe number of calories your body needs at complete rest to maintain vital functions like breathing, circulation, and cell production.: eating below this number causes your body to break down muscle and organ tissue for fuel. To calculate how many calories you actually need including activity, multiply BMRThe number of calories your body needs at complete rest to maintain vital functions like breathing, circulation, and cell production. by an activity factor to get TDEETotal calories burned per day, including BMR plus physical activity and the thermic effect of food. Used for weight management.. Mifflin-St Jeor (1990) is the most validated for the general population, developed using a sample of 498 healthy adults. Harris-Benedict (1919, revised 1984) tends to overestimate BMRThe number of calories your body needs at complete rest to maintain vital functions like breathing, circulation, and cell production. by 5% or more on average. Katch-McArdle is most accurate for lean athletes with known body fat % because it uses lean body mass rather than total weight — this eliminates the error from estimating BMRThe number of calories your body needs at complete rest to maintain vital functions like breathing, circulation, and cell production. for overweight individuals where fat mass inflates the weight-based formulas. BMRThe number of calories your body needs at complete rest to maintain vital functions like breathing, circulation, and cell production. naturally declines with age by approximately 2% per decade after age 20, primarily due to sarcopenia (age-related muscle loss). However, this decline can be significantly slowed with consistent resistance training. Body composition changes explain most of the age-related BMRThe number of calories your body needs at complete rest to maintain vital functions like breathing, circulation, and cell production. decrease, not aging itself. Women typically have a 5–10% lower BMRThe number of calories your body needs at complete rest to maintain vital functions like breathing, circulation, and cell production. than men of the same age and weight because they carry proportionally more body fat and less muscle mass. The thermic effect of food adds roughly 10% on top of BMRThe number of calories your body needs at complete rest to maintain vital functions like breathing, circulation, and cell production., and physical activity accounts for the rest of total daily energy expenditure.

Frequently Asked Questions

Sources & References