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Professional BMR Calculator

Calculate your Basal Metabolic Rate (calories burned at complete rest) using Mifflin‑St Jeor, Harris‑Benedict, and Katch‑McArdle formulas.

If known, provides a more accurate BMR based on lean body mass.

Mifflin‑St Jeor BMR (Recommended)

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All Formula Results (kcal/day)

Mifflin‑St Jeor —
Harris‑Benedict (Revised) —
Katch‑McArdle (Lean Mass) —

🧬 Lean Body Mass: —

📊 What Your BMR Means

From BMR to Total Daily Energy Expenditure (TDEE)

Activity Level Multiplier Description
Sedentary1.2Little or no exercise, desk job
Lightly Active1.375Light exercise 1‑3 days/week
Moderately Active1.55Moderate exercise 3‑5 days/week
Very Active1.725Hard exercise 6‑7 days/week
Extremely Active1.9Physical job + intense training

Understanding Your Basal Metabolic Rate (BMR)

Your Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest—just to keep your heart beating, lungs breathing, and cells functioning. It's the foundation of your total daily energy expenditure (TDEE) and a crucial metric for weight management. This Professional BMR Calculator provides BMR estimates using three validated formulas, helping you understand your body's baseline energy needs.

The Science Behind BMR Formulas

  • Mifflin‑St Jeor (1990): The most accurate formula for healthy, non‑obese adults. It's the standard used by dietitians and fitness professionals.
  • Harris‑Benedict (Revised, 1984): An updated version of the classic 1919 formula. Slightly higher estimates than Mifflin‑St Jeor.
  • Katch‑McArdle (1996): Uses lean body mass (weight minus fat) to calculate BMR. Most accurate if you know your body fat percentage, especially for lean or muscular individuals.

💡 Why BMR Declines with Age

After age 30, BMR decreases by approximately 1‑2% per decade, largely due to loss of muscle mass. Strength training and adequate protein intake can help preserve lean tissue and maintain a higher metabolic rate.

How to Use Your BMR for Weight Goals

Multiply your BMR by an activity factor (see table) to get your TDEE—the calories you burn in a day. To lose weight, create a modest deficit (typically 300‑500 kcal below TDEE). To gain muscle, add a surplus (200‑300 kcal above TDEE). Remember, BMR is just the starting point; actual needs vary based on genetics, hormones, and non‑exercise activity (NEAT).

Factors That Influence BMR

  • Body Composition: Muscle is more metabolically active than fat. Higher lean mass increases BMR.
  • Genetics: Some people are naturally "high" or "low" metabolizers.
  • Hormones: Thyroid hormones, cortisol, and sex hormones affect metabolic rate.
  • Climate: Living in very cold or hot environments can slightly increase BMR.

Frequently Asked Questions

Is BMR the same as metabolism?

BMR is the largest component of metabolism (60‑75%), but total metabolism also includes the thermic effect of food and physical activity.

Can I increase my BMR?

Yes. Building muscle through resistance training is the most effective way. Eating enough protein and getting quality sleep also support a healthy BMR.

Why does my BMR seem low?

BMR naturally varies. If you've lost weight, your BMR decreases. Chronic dieting can also lower BMR (adaptive thermogenesis). Focus on sustainable habits.

Should I eat below my BMR to lose weight?

No. Eating below BMR for extended periods can lead to muscle loss, metabolic slowdown, and nutrient deficiencies. Aim for a moderate deficit from TDEE instead.

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