Question 1

What is basal metabolic rate (BMR)?

Accepted Answer

Basal metabolic rate (BMR) is the number of calories your body burns at complete rest to maintain basic life-sustaining functions like breathing, blood circulation, cell production, and temperature regulation. BMR accounts for 60-75% of your total daily calorie expenditure. For most adults, BMR falls between 1,200 and 2,400 calories per day, depending on age, sex, weight, height, and body composition. Key point: BMR is measured under strict conditions - 12 hours of fasting, 8 hours of sleep, in a temperature-controlled room. In practice, your Resting Metabolic Rate (RMR) is nearly identical (within 5%) and is what most calculators estimate.

Question 2

What is the difference between BMR and TDEE?

Accepted Answer

BMR is the calories you burn at complete rest. TDEE (Total Daily Energy Expenditure) is the total calories you burn including all activity throughout the day. TDEE = BMR + Activity BMR: 1,700 cal (what you burn lying in bed all day) Activity multiplier: 1.55 (moderate exercise 3-5 days/week) TDEE: 1,700 x 1.55 = 2,635 cal For weight management: Always base your calorie goals on TDEE, not BMR. Eating below your BMR long-term can cause metabolic adaptation, muscle loss, and nutrient deficiencies. Use our TDEE & Macro Calculator for detailed daily calorie and macro targets.

Question 3

What is the Katch-McArdle formula and when should I use it?

Accepted Answer

The Katch-McArdle formula estimates BMR using lean body mass (LBM) instead of total body weight: BMR = 370 + (21.6 x lean body mass in kg) When to use Katch-McArdle: You know your body fat percentage from a reliable method (DEXA, hydrostatic weighing, or calipers) You have significantly more or less muscle than average for your size You're a trained athlete or bodybuilder Why it's more accurate for some people: Muscle tissue burns ~6 cal/lb/day while fat tissue burns ~2 cal/lb/day. The Katch-McArdle formula accounts for this difference, making it more precise for people who know their body composition. Don't know your body fat percentage? Use our Body Fat Calculator to estimate it.

Question 4

How do I calculate BMR using the Mifflin-St Jeor equation?

Accepted Answer

The Mifflin-St Jeor equation (1990) is considered the most accurate BMR formula for the general population when body fat percentage is unknown: Men: BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age) + 5 Women: BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age) - 161 Example (30-year-old male, 180 lbs, 5'10"): Weight: 180 lbs = 81.6 kg Height: 70 inches = 177.8 cm BMR = (10 x 81.6) + (6.25 x 177.8) - (5 x 30) + 5 BMR = 816 + 1,111 - 150 + 5 = 1,782 calories/day The American Dietetic Association recommends Mifflin-St Jeor over older formulas like Harris-Benedict for its improved accuracy across diverse populations.

Question 5

How does the Mifflin-St Jeor equation compare to Harris-Benedict?

Accepted Answer

Both formulas estimate BMR, but they differ in accuracy and approach: Feature Mifflin-St Jeor (1990) Harris-Benedict (Revised 1984) Accuracy Within 5% for ~82% of people Within 5% for ~69% of people Tendency Slightly conservative Tends to overestimate by 5-15% Best for General population (recommended) Historical comparison Recommendation: Use Mifflin-St Jeor as your primary estimate. The Harris-Benedict result is included for comparison. If you know your body fat percentage, the Katch-McArdle formula will be the most accurate of all three.

Question 6

What factors affect my BMR?

Accepted Answer

Several factors influence your basal metabolic rate, some controllable and some not: Factors You Can Influence: Muscle mass: Each pound of muscle burns ~6 cal/day vs ~2 cal/day for fat Body weight: Larger bodies require more energy to maintain Exercise habits: Regular resistance training increases lean mass over time Nutrition: Severe caloric restriction can reduce BMR by 15-20% Factors You Cannot Change: Age: BMR decreases ~2-3% per decade after 20 Sex: Males typically have 5-10% higher BMR due to greater lean mass Genetics: Individual variation of ~200-300 calories exists Height: Taller people have higher BMR due to more tissue The best strategy to maintain a higher BMR: Build and maintain muscle through resistance training, eat adequate protein (1.6-2.2 g/kg), and avoid prolonged severe calorie deficits.

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What is basal metabolic rate?

Quick Facts

BMR Calculator FAQ

What is basal metabolic rate (BMR)?

What is the difference between BMR and TDEE?

What is the Katch-McArdle formula and when should I use it?

How do I calculate BMR using the Mifflin-St Jeor equation?

How does the Mifflin-St Jeor equation compare to Harris-Benedict?

What factors affect my BMR?

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