What Is Basal Metabolic Rate?
Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest to maintain essential functions such as breathing, circulation, cell production, and temperature regulation. It represents the minimum energy your body needs to survive if you were to lie still for 24 hours.
BMR is the foundation of all calorie calculations. Once you know your BMR, you multiply it by an activity factor to get your Total Daily Energy Expenditure (TDEE), which is the actual number of calories you burn on a typical day. From there, you adjust for your goal: eat less to lose weight, or eat more to gain.
What This Calculator Does
This calculator estimates your BMR using three established formulas and lets you select the one best suited to your situation. It also calculates your TDEE and provides calorie targets for weight loss, maintenance, and weight gain.
Inputs Required
- Sex: Biological sex affects both formulas used
- Age: Metabolic rate declines gradually with age
- Height: In feet and inches or centimeters
- Weight: In pounds or kilograms
- Activity Level: How active you are on a typical day
- Formula: Choose Mifflin-St Jeor, Harris-Benedict, or Katch-McArdle
- Body Fat % (Katch-McArdle only): Required to calculate lean body mass
Outputs Provided
- BMR: Calories burned per day at complete rest
- TDEE: Total calories burned including your activity
- Calorie Targets: Adjusted values for weight loss, maintenance, and weight gain
- Formula Comparison: BMR results from all three formulas side by side
How the Calculation Works
Mifflin-St Jeor Equation (1990)
Male: BMR = 10 x weight (kg) + 6.25 x height (cm) - 5 x age + 5
Female: BMR = 10 x weight (kg) + 6.25 x height (cm) - 5 x age - 161
This is the most widely recommended formula and is considered the most accurate for the general population. A 2005 review in the Journal of the American Dietetic Association found it predicted resting metabolic rate more accurately than older equations in most groups.
Harris-Benedict Equation (Revised 1984)
Male: BMR = 88.362 + 13.397 x weight (kg) + 4.799 x height (cm) - 5.677 x age
Female: BMR = 447.593 + 9.247 x weight (kg) + 3.098 x height (cm) - 4.330 x age
Originally published in 1919 and revised by Roza and Shizgal in 1984, the Harris-Benedict equation is one of the oldest BMR formulas. It tends to overestimate BMR slightly compared to Mifflin-St Jeor, particularly in overweight individuals.
Katch-McArdle Equation
BMR = 370 + 21.6 x Lean Body Mass (kg)
Lean Body Mass = Total Weight x (1 - Body Fat %)
This formula is based on lean body mass rather than total weight, making it more accurate for people who know their body fat percentage. It does not distinguish between male and female because sex differences are already accounted for through lean mass.
Activity Multipliers (TDEE)
TDEE = BMR x Activity Factor
- Sedentary (x1.2): Desk job with little to no exercise
- Lightly active (x1.375): Light exercise 1 to 3 days per week
- Moderately active (x1.55): Moderate exercise 3 to 5 days per week
- Very active (x1.725): Hard exercise 6 to 7 days per week
- Extra active (x1.9): Very hard daily exercise plus a physical job
How to Use the Calculator
- Select imperial or metric units
- Select your biological sex
- Enter your age, height, and weight
- If using Katch-McArdle, enter your body fat percentage
- Select your activity level honestly
- Choose your preferred formula
- View your BMR, TDEE, and calorie targets instantly
Example Calculation
A 30-year-old male, 5 feet 10 inches (177.8 cm), 170 lbs (77.1 kg), moderately active:
- Mifflin-St Jeor BMR: 10(77.1) + 6.25(177.8) - 5(30) + 5 = 1,737 cal/day
- Activity factor (x1.55): 1,737 x 1.55 = 2,692 cal/day (TDEE)
- Weight loss target: 2,692 - 500 = 2,192 cal/day
- Weight gain target: 2,692 + 500 = 3,192 cal/day
Real World Scenarios
Starting a Weight Loss Plan
A 40-year-old woman wants to lose weight but has no idea where to start with calories. She enters her details and discovers her TDEE is 1,950 calories. She sets a daily target of 1,450 calories for a 500-calorie daily deficit, aiming for roughly 1 pound of fat loss per week.
Muscle Building Program
A 25-year-old man training for muscle gain uses the Katch-McArdle formula after measuring his body fat at 14%. This gives him a more accurate BMR based on lean mass. He sets his intake 300 calories above TDEE to support muscle growth while minimizing fat gain.
Recovery After Illness
Someone recovering from surgery and on reduced activity uses the sedentary multiplier to estimate their reduced calorie needs during recovery. Knowing their BMR helps them avoid overeating during a period when they are largely inactive.
Why This Calculation Matters
Without knowing your BMR and TDEE, any calorie target you set is essentially a guess. BMR is the baseline that makes personalized nutrition planning possible. Whether you are trying to lose fat, build muscle, improve athletic performance, or simply maintain a healthy weight, your BMR is the number that makes the rest of the math work.
BMR also changes over time. As you lose weight, gain muscle, or age, your BMR shifts. Recalculating periodically ensures your nutrition plan stays aligned with your actual metabolic needs.
Common Mistakes to Avoid
- Confusing BMR with TDEE: BMR is calories at complete rest. TDEE is your actual daily burn including movement. You should eat near your TDEE to maintain weight, not your BMR
- Overestimating activity level: Most people overestimate how active they are. This is the most common cause of a stalled diet. When uncertain, choose one level lower than you think
- Not recalculating after weight changes: Every 10 to 15 pounds of weight change will shift your BMR meaningfully. Recalculate to keep your targets accurate
- Treating the result as exact: BMR formulas estimate a population average. Individual metabolism can vary by 10 to 15 percent. Adjust your intake based on real-world results over 2 to 3 weeks