BMR Calculator

Basal Metabolic Rate (BMR) is the number of calories your body needs to maintain basic life-sustaining functions such as breathing, circulation, and cell production. Understanding your BMR is the foundation for building any calorie-based nutrition plan.

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What Is Basal Metabolic Rate?

Your Basal Metabolic Rate (BMR) represents the minimum number of calories your body requires to perform essential physiological functions while at complete rest. These functions include maintaining body temperature, powering brain activity, circulating blood, and supporting cellular repair. BMR typically accounts for 60-75% of your total daily energy expenditure, making it by far the largest component of the calories you burn each day.

Several factors influence BMR, including age, sex, height, weight, and body composition. Muscle tissue is more metabolically active than fat tissue, which is why individuals with higher lean body mass tend to have higher BMRs.

The Formulas

Mifflin-St Jeor Equation (recommended)

  • Men: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) + 5
  • Women: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) − 161

Revised Harris-Benedict Equation

  • Men: BMR = 13.397 × weight (kg) + 4.799 × height (cm) − 5.677 × age (years) + 88.362
  • Women: BMR = 9.247 × weight (kg) + 3.098 × height (cm) − 4.330 × age (years) + 447.593

The Mifflin-St Jeor equation is considered the most accurate for most populations according to the Academy of Nutrition and Dietetics.

How to Use Your BMR

Your BMR alone is not your daily calorie need. To estimate Total Daily Energy Expenditure (TDEE), multiply BMR by an activity factor ranging from 1.2 (sedentary) to 1.9 (very active). Use TDEE as the baseline for setting calorie targets for fat loss, maintenance, or muscle gain.

Limitations

BMR equations are population-based estimates with a typical error margin of 5-10%. Individual variations in genetics, hormonal status, and body composition can cause your actual BMR to differ. For a precise measurement, indirect calorimetry in a clinical setting is the gold standard. Consult a registered dietitian or healthcare provider before designing a calorie plan around your BMR.

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Frequently Asked Questions

What is the difference between BMR and RMR?
BMR (Basal Metabolic Rate) is measured under strict resting conditions, typically after 8 hours of sleep and 12 hours of fasting. RMR (Resting Metabolic Rate) is measured under less restrictive conditions and is usually 10-20% higher. For practical purposes, the two are often used interchangeably.
Why does BMR decrease with age?
BMR declines with age primarily because of the gradual loss of lean muscle mass (sarcopenia) and hormonal changes. After age 30, most people lose approximately 3-5% of muscle mass per decade if they do not engage in resistance training. Maintaining muscle through exercise can help offset this decline.
Can I increase my BMR?
Yes. Building lean muscle mass through resistance training is the most effective way to raise your BMR because muscle tissue burns more calories at rest than fat tissue. Staying well-hydrated, getting adequate sleep, and eating enough protein also support a healthy metabolic rate.
Should I eat below my BMR to lose weight?
Eating below your BMR for extended periods is generally not recommended because it can slow metabolism, cause muscle loss, and lead to nutrient deficiencies. A moderate deficit below your TDEE (not BMR) of 300-500 calories per day is a safer, more sustainable approach to fat loss.
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