Health

BMR Calculator

Calculate your Basal Metabolic Rate using two clinically validated formulas. Compare Mifflin-St Jeor and Harris-Benedict results side by side.

Quick Answer

BMR (Basal Metabolic Rate) is the calories your body burns at rest just to stay alive. The Mifflin-St Jeor formula for men is 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5 (subtract 161 instead for women). A typical BMR is 1,400–1,800 cal/day for women and 1,600–2,000 cal/day for men. To find total daily calories, multiply BMR by an activity factor (1.2–1.9) to get your TDEE.

Biological Sex

Age

years

Height

Weight

lbs

Your BMR Results

Mifflin-St Jeor (Recommended)

1,737

calories/day at rest

Harris-Benedict (Comparison)

1,804

calories/day at rest

Difference: 67 calories/day (4% variance). The Mifflin-St Jeor equation is recommended by the Academy of Nutrition and Dietetics as it has been shown to be more accurate within ±10% for most individuals.

Formula Breakdown

Mifflin-St Jeor (1990)

10 x 77.1kg + 6.25 x 177.8cm - 5 x 30 + 5 = 1737

Harris-Benedict (Revised 1984)

88.362 + 13.397 x 77.1kg + 4.799 x 177.8cm - 5.677 x 30 = 1804

Estimated TDEE by Activity Level

Based on your Mifflin-St Jeor BMR of 1,737 cal/day

Sedentary— Little or no exercise

2,084cal/day

Lightly Active— Light exercise 1-3 days/week

2,388cal/day

Moderately Active— Moderate exercise 3-5 days/week

2,692cal/day

Very Active— Hard exercise 6-7 days/week

2,996cal/day

Extremely Active— Athlete or physical job + training

3,300cal/day

Get exact TDEE + macro breakdown →

Important: This calculator provides estimates based on population-level formulas. Individual metabolic rates vary based on body composition, genetics, hormones, and medical conditions. These results are not a substitute for professional medical or nutritional advice. Consult a healthcare provider before making dietary changes.

About This Tool

The BMR Calculator computes your Basal Metabolic Rate using two clinically validated formulas and presents them side by side so you can see how they compare. Your BMR represents the minimum number of calories your body needs each day just to maintain basic physiological functions like breathing, blood circulation, cell production, and temperature regulation while completely at rest.

Mifflin-St Jeor vs. Harris-Benedict

The Mifflin-St Jeor equation was published in 1990 and is recommended by the Academy of Nutrition and Dietetics as the most reliable formula for estimating resting metabolic rate. It was validated against indirect calorimetry and showed prediction accuracy of approximately 82% for non-obese individuals. The Harris-Benedict equation, originally published in 1919 and revised in 1984, was the clinical standard for decades but tends to overestimate calorie needs by 5-15%, particularly in overweight individuals. We show both results so you can see the range and use the most appropriate estimate for your situation.

BMR vs. TDEE: Understanding the Difference

BMR measures calories burned at complete rest — imagine lying in bed all day without moving. It typically accounts for 60-75% of your total daily energy expenditure. TDEE (Total Daily Energy Expenditure) adds the calories you burn through physical activity, the thermic effect of food (energy used during digestion), and non-exercise activity thermogenesis (NEAT). For weight management, your TDEE is the number that matters because it represents your actual daily calorie needs. BMR is the foundation that TDEE is built upon.

What Affects Your BMR

Several factors influence your basal metabolic rate beyond age, sex, height, and weight. Muscle mass is a major driver — each pound of muscle burns roughly 6 calories per day at rest compared to 2 calories per pound of fat. This is why strength training can raise your BMR over time. Hormones (particularly thyroid hormones) play a significant role; hypothyroidism can reduce BMR by 10-15%. Genetics account for an estimated 40% of the variation in metabolic rates between individuals. Extreme calorie restriction can lower BMR by 15-20% through a process called metabolic adaptation, which is why crash diets often backfire.

Limitations of BMR Formulas

Both formulas use population averages and can be off by 10% or more for individuals. They are least accurate for very muscular individuals (formulas underestimate), very lean individuals, elderly populations, and people with metabolic disorders. The Katch-McArdle formula, which uses lean body mass, can be more accurate for athletic individuals but requires knowing your body fat percentage. For the most precise measurement, indirect calorimetry (breathing into a metabolic analyzer) is the gold standard, though it is typically only available in clinical settings.

Frequently Asked Questions

What is a normal BMR for my age and gender?

Average BMR for adult women ranges from 1,200 to 1,600 calories per day, while adult men typically range from 1,600 to 2,000 calories per day. BMR decreases with age at roughly 1-2% per decade after age 20, primarily due to loss of lean muscle mass. A 25-year-old man at 180 lbs might have a BMR of 1,850 cal/day, while at 55 the same man might have a BMR closer to 1,650 cal/day.

Can I increase my BMR?

Yes. Building muscle through resistance training is the most effective way to raise BMR since muscle tissue is more metabolically active than fat. Each pound of muscle added burns approximately 6 additional calories per day at rest. High-intensity interval training (HIIT) can temporarily boost metabolic rate for 24-48 hours after exercise. Adequate protein intake (0.7-1g per pound of body weight) supports muscle preservation. Avoiding crash diets prevents metabolic adaptation, which can lower BMR by 15-20%.

Which BMR formula is more accurate?

The Mifflin-St Jeor equation is considered the most accurate for the general population and is recommended by the Academy of Nutrition and Dietetics. It was developed using a more diverse, modern population sample and predicts resting metabolic rate within 10% for approximately 82% of non-obese individuals. The Harris-Benedict equation tends to overestimate by 5-15%, especially for overweight individuals. For athletes with low body fat, the Katch-McArdle formula (which uses lean body mass) may be more accurate.

Why does BMR differ between men and women?

Men generally have higher BMR than women primarily because they carry more lean muscle mass and less body fat on average. Muscle tissue requires more energy to maintain than fat tissue. Hormonal differences also play a role: testosterone promotes muscle development and a higher metabolic rate, while estrogen promotes fat storage. The Mifflin-St Jeor formula accounts for this with different constants: +5 for men and -161 for women.

How does BMR relate to weight loss?

BMR establishes the minimum calories your body needs. Eating below your BMR for extended periods can trigger metabolic adaptation, where your body slows its metabolism to conserve energy, making weight loss harder. Most dietitians recommend eating at or above your BMR but below your TDEE for sustainable weight loss. For example, if your BMR is 1,500 and your TDEE is 2,200, eating 1,700 calories creates a healthy 500-calorie deficit without dipping below your BMR.

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